Associated Press

After surviving a long primary season, Mitt Romney stands alone following its rapid conclusion, as opponent Rick Santorum ended his campaign in April, Newt Gingrich dropped out at the beginning of May, and Ron Paul effectively ended his presidential campaign on May 14. With his eyes on the White House prize now, Romney has turned his attention to his next challenge — picking a running mate.

Marco Rubio
Associated Press

At the beginning of April, Paddypower, which gives odds on political bets, opened betting on a possible VP pick for the Romney ticket. Sen. Marco Rubio, R-Fla., shot to the top slot. Rubio, who has endorsed Romney, said April 4, "I'm not going to be the vice president." Rubio won the CPAC 2012 vice-presidential choice poll overwhelmingly. However, a Hotline On Call insiders poll shows enthusiasm for Rubio waning.

Positives: The Christen Science Monitor calls Rubio "young, charismatic and serious about policy." His Hispanic heritage would also be a big boon.

Negatives: Why settle for No. 2 when he could be No. 1 in a few years? Conservative writer Ann Coulter says that he should wait. A loss on a Romney ticket could damage his future prospects.

Chris Christie
Associated Press

New Jersey Gov. Chris Christie was floated as a possible presidential candidate, but he strongly rejected every push in that direction, to the point that he joked about having to commit suicide to convince people he was serious. "The person that picked me as vice president would have to be sedated," Christie said last June. He later said, "If Gov. Romney were to come and talk to me about it, I would listen because I love my party enough and I love my country enough to listen."

Positives: Christie is a strong social conservative, pro-life and a staunch opponent to gay marriage. His no-nonsense candor pleases some. His pick could reassure people who think Romney is squishy on entitlement reforms and budget cuts.

Negatives: A recent Yahoo article says Romney won't pick Christie because the two are too similar – white, middle-aged governors from Northeastern states. Christie might also face questions from the right on gun control, immigration cases and his views on global warming.

Paul Ryan
Associated Press

After Rep. Paul Ryan, R-Wis., and Mitt Romney campaigned together in Wisconsin (resulting in a win for Romney in the state), the chairman of the House Budget Committee has been attracting more VP buzz. Ryan has taken the lead in challenging President Obama over his budget choices, and a possible trial balloon speech attracted praise from conservatives.

Positives: Ryan has been targeted by Obama before, most recently at the Associated Press luncheon, and he's not hesitant to push back when attacked. The Washington Post calls his attack-dog rhetoric perfect for a vice presidential nominee. Since Obama will seek to make Ryan's budget a central campaign issue, having the foremost expert on the plan as part of the ticket makes sense, George Will says.

Negatives: As The Daily Beast points out, Ryan would have to give up his seat in the House for a vice presidential bid, which might make him less inclined to put his name on the ticket. Additionally, putting Ryan on the ticket would make the Romney-Ryan budget connection absolute.

Rob Portman
Associated Press

With Ryan's Wisconsin triumph in the past, pundits have turned to Sen. Rob Portman, R-Ohio, as the latest darling in the veepstakes. Paul Begala at The Daily Beast is positive Romney will pick Portman — someone who "will not overshadow him, someone who will not blow up in his face, and someone who will fit Romney's play-it-safe, buttoned-up image." Major Garrett, a correspondent for National Journal, is also putting his money on Portman.

Positives: According to Garrett, Romney likes and respects Portman, Portman wants the job, Portman is ready for the job and Portman has already been vetted, having worked as the U.S. trade representative in 2005 and as the Office of Management and Budget director in 2006.

Negatives: The Daily Beast calls Portman "a dull and uncharismatic fiscal conservative, just like Mitt Romney." If the party is looking to boost voter enthusiasm, that might not be the best direction to go. In 2008, the Washington Post's Chris Cillizza called Portman a "Bush guy" who wouldn't be a good attack dog.

Susana Martinez
Associated Press

“Don’t know her, but on paper I think she looks very impressive,” veteran GOP strategist Mike Murphy, a one-time aide to Mitt Romney, told The Daily Caller in December. Romney dropped the first-term Republican governor's name during an interview on Fox News, where he also mentioned the governors of New Jersey, Louisiana and South Carolina as possible running mates.

Positives: Martinez is the first female Hispanic governor in the U.S., the first female governor of New Mexico and the most popular of the freshman Republican governors. She has an approval rating of more than 50 percent and she may help Romney with women and Hispanics.

Negatives: "It's humbling, but I'm not interested," New Mexico Gov. Susana Martinez said. “I have no intentions of doing anything different other than being governor."

Bob McDonnell
Associated Press

Gov. Martin O'Malley, D-Md., called Gov. Bob McDonnell of Virginia possibly a better job creator than Mitt Romney, saying, "I think he's a very skilled leader, and he does an able job as the head of the Republican Governors Association." McDonnell endorsed Romney in January.

Positives: He's a Southerner and he's popular in a traditionally Republican state that went for Obama in 2008. He's also a social conservative and job creator, and he's been building a national fundraising network.

Negatives: A controversial abortion bill regarding ultrasounds may dampen enthusiasm for McDonnell. A 1989 master's thesis about working mothers may also present trouble.

Nikki Haley
Associated Press

As Romney trails behind Obama with women voters, adding a female vice president to the ticket may help him bridge that gap. The first woman governor of South Carolina and the second Indian-American governor in the U.S. (the first being Bobby Jindal, R-La.), Haley endorsed Romney in December, but it didn't help Romney in South Carolina, when he lost the state to Newt Gingrich in January.

Positives: Elected in the Republican wave of 2010, Haley could bring tea party credentials and enthusiasm to the ticket. U.S. News wrote that as a "woman and daughter of immigrants from India, she's practiced conservative principles in working to fix the state's budget," which may help draw conservative voters.

Negatives: At the beginning of April, Haley said she would turn down the job if offered. "I made a promise to the people of this state," she told ABC News, "and I think that promise matters. And I intend to keep it." Joanne Bamberger at The Huffington Post wrote that Haley won't be chosen due to "bad Palin mojo."

Rand Paul
Associated Press

After a February filled with talk of a Mitt Romney-Ron Paul alliance, pundits wondered if the lack of attacks between the two men signaled a strategy to land Ron Paul's son, Sen. Rand Paul, R-Ky., on a Romney ticket as the VP pick. Rand Paul has said, "it would be an honor to be considered."

Positives: As Human Events points out, Rand Paul may be able to bring a good deal of his father's support to the ticket, and he might be more willing to spend four or eight years in the VP slot than his father. Rand Paul could also bring the tea party vote for Romney.

Negatives: As a junior Senator, Rand Paul has only been in office since 2010, making him something of a newbie on the political scene. Comments he has made throughout his time in the spotlight, including one made during the BP oil spill, have earned him criticism.

John Thune
Associated Press

Sen. John Thune from South Dakota made the Washington Post's Veepstakes 2012 inaugural edition, but he's been flying under the radar since. In 2011, he declined to run for president, saying he wanted to remain "in the trenches of the United States Senate."

Positives: The Washington Post ranks him as a "Plains state Senator with good looks and an almost-impeccable conservative reputation." Such a reputation may help draw voters who still feel squishy about Romney's positions (or past positions) on some issues.

Negatives: A 2011 Time profile stated that Thune would have problems as a national candidate due to the 2008 bank bailout vote, earmarks, low profile, small political operation and the possible lack of the "fire in the belly" campaign passion.

John Kyl
Associated Press

Sen. John Kyl, R-Ariz., who is not running for reelection, has won the praise of a Romney fan — conservative political commentator Ann Coulter. In April, Coulter told Bill O'Reilly that Rubio should not be the 2012 VP candidate, and that Kyl would be a better option.

Positives: According to Coulter, Kyl is "very appealing," "not scary on TV," and the fourth most conservative Senator. Kyl is known for his foreign policy stances and could bolster Romney's foreign policy platform.

Negatives: In the interview, O'Reilly countered by saying Kyl wouldn't bring any votes to the ticket, being from Arizona. "I wouldn't close my mind to being a vice presidential candidate," Kyl said at a news conference in Arizona when he announced his retirement. "However, having said that, I expect the chances of that are zero."

Allen West
Associated Press

Rep. Allen West, R-Fla., took office in 2011, riding the same wave as Nikki Haley, Rand Paul, and others. He is a veteran, having served in the Army for more than 20 years, including deployments in Iraq. West has been floated as a possible VP pick by Sarah Palin and Herman Cain, while Nikki Haley listed West as worth considering.

The positives and negatives of Alan West depend on your perspective. Some may be drawn to his blunt style, while others may be put off. For example, when he received a letter from the Council on Islamic-American Relations requesting he cut relations with "anti-Islamic extremists," West's response was this: "NUTS!" Politico has a breakdown of West's top 10 most memorable lines, so people can see where they fall.

"I've never been out on a dinner date with [Romney] if that's what you're asking me," West said in a CNN interview. "So I don't know if I would like him. But I think that we'd have to sit down and discuss some things."

Mitch Daniels
Associated Press

After declining to run for the presidential slot in 2012, Indiana's popular governor has been touted as a VP possibility. However, he has also indicated that he's not interested in the job.

Positives: Aaron Blake at the Washington Post calls Daniels the "adult in the room," saying he's both conservative and pragmatic, and focuses on what's important and doable. A January poll showed Daniels with a 65 percent approval rating in his home state, what Blake calls a "nearly unthinkable number for most governors in tough economic times."

Negatives: As those pushing Daniels to run for president found, it's impossible to run a candidate who's not interested, and on March 19, Fox 59 quoted Daniels as saying he's not.

Tim Pawlenty
Associated Press

Former presidential candidate and former Minnesota Gov. Tim Pawlenty, who endorsed Romney in September 2011, may offer some benefits for Romney in the general election.

Positives: calls Pawlenty "likable, articulate, confident and good-hearted," and says he has a "presence that young people, Independents, Populist Conservatives, suburbanites, women and mavericks can appreciate."

Negatives: MSNBC calls Pawlenty a bland (if safe) pick, which may not be exactly what the base needs. However, Pawlenty also said recently that he's taken himself off the list.

Kelly Ayotte
Associated Press

Sen. Kelly Ayotte, R-N.H., previously served as the attorney general of New Hampshire. Romney mentioned her as a potential running mate in November 2011, saying she was one of about 15 people he would consider as VP. Ayotte endorsed him around the same time, saying he is the "one person in [the GOP field] who is prepared to lead the United States of America."

Positives: Like Haley or Martinez, Ayotte could bring over women voters. National Journal calls Ayotte a "compelling choice," and praises her for winning plaudits as the first female attorney general. She also beat a sitting Democratic congressman by a 23-point margin, and could carry the swing state of New Hampshire.

Negatives: Roll Call points out that New Hampshire governor John Lynch is a Democrat, and could appoint an interim replacement from his party should a Romney/Ayotte ticket win the presidency.

Bobby Jindal
Associated Press

The first Indian-American governor in the U.S. and the current governor of Louisiana, Jindal also served in the U.S. House, and has attracted the kudos of fans in the political world. Sen. John McCain mentioned Jindal as a possibility, while GOP strategist Mark MicKinnon told NPR that Jindal could be a long shot that could excite people.

Positives: Like Paul Ryan, pundit George Will considers Jindal capable of bringing intellectual firepower to the VP spot. McKinnon also says Jindal's "amazing track record on health care issues" could make him an interesting pick. LSU political science professor Robert Hogan said Jindal could bring conservatives to Romney.

Negatives: After endorsing Rick Perry in September 2011, Jindal said he "will not be the VP," and that he wants "to be governor of the great state of Louisiana." How his sentiments may have changed now that Perry is gone and Romney is the almost-certain nominee remain to be seen. In an April 6 post, Jeff Crouere wrote at that Jindal should not be considered, and that he "only plays a conservative on TV."

Condoleezza Rice
Associated Press

Former United States Secretary of State Condoleezza Rice has been out of the political spotlight for a while, but Huffington Post writer Keith Koeneman is convinced she'd be the perfect choice as Romney's VP. " Rice would complement Romney with respect to race and gender, but her qualifications as a vice president go far beyond these demographic details," he writes. Van Jones, a former environmental advisor to the Obama White House, agree.

Positives: Koeneman lists Rice's intelligence, gravitas, experience and diversity as boons in the VP slot. Jones says she brings foreign policy experience. "You want to do something bold, put Condoleezza Rice on the ticket and watch the Obama campaign go crazy," Jones said.

Negatives: Putting Rice on the ticket might allow the Obama administration to run against former President Bush rather than Romney. Additionally, Rice told Fox and Friends that she prefers policy to politics. "I think we should go another direction and find somebody who really wants to be in elected office, Rice said. "How many ways can I say it? Not me."

Mike Huckabee
Associated Press

CBN News chief political correspondent David Brody calls former presidential candidate Mike Huckabee the "guy to seal the deal" for Romney. However, when asked if he'd consider being VP, Huckabee said it's best not to buy the corsage for the prom until you get a date.

Positives: Huckabee, Brody suggests, could help Romney win evangelicals, tea partiers and white middle class voters. Plus, he adds, Huckabee has already ben vetted, which would mean fewer election surprises for the Romney team to deal with.

Negatives: While Romney and Huckabee weren't the best of friends in 2008, Romney just appeared on Huckabee's new radio show. However, at a recent fundraiser, Romney warned donors about a brokered convention resulting in a Huckabee-Palin ticket. Can time heal all wounds, or does animosity still bubble under the surface?

Haley Barbour
Associated Press

In April 2011, Gov. Haley Barbour, R-Miss., announced he would not run for president. Barbour is a former chairman of the Republican National Committee and wields a lot of power in the party and in his state.

Positives: A 2009 Slate piece suggests Haley, the GOP's Mr. Fix-It, would be able to lead the party through an era of rebuilding. "He's an unusual combination of someone who's really good on policy, really good on politics, and really good on TV," says Democratic lobbyist Anthony Podesta. "And everybody likes him."

Negatives: In March, Barbour said he does not regret avoiding the presidential race, and is not interested in being VP. "I don't think I'm a good running mate for anybody," he told Fox News. Additionally, Barbour suggests he wouldn’t help carry more than a few states in the presidential election, which would not help Romney.

Scott Walker
Associated Press

The embattled Wisconsin governor, currently facing a recall election for undertaking major financial changes in his state, has been floated as a possible VP pick by former state lawmaker and UW-Milwaukee political science professor Mordecai Lee and others. Choosing him would be an act of political courage, Howard Foster wrote at The Huffington Post.

Positives: "He's just really put his career on the line for what the Republican party believes in," Lee said. "I'm not sure many Wisconsinites realize it, but he's a national hero." The Daily Caller suggests his battle with state-level pay and benefits for public employees could strike a chord during this era of hurting state budgets.

Negatives: Walker was wounded by strident union attacks during the height of the public union bargaining rights debate. This could hurt a national ticket. Additionally, Walker has said he plans on being governor for the next four years, and that he's invested too much time and effort to walk away.

Sarah Palin
Associated Press

Suggested by the one who knows her best on the campaign trail, Sen. John McCain, R-Ariz., said on a recent CBS This Morning, "I think it should be Sarah Palin." Whether or not he was joking is debatable. He went on to say that there was a "wealth of talent" in the GOP field, including Rubio, Christie and Jindal.

Palin has plenty of staunch defenders and critics. Like West, whether she is a good or bad political pick probably depends on your point of view. She can create enthusiasm with some, but may fire up anti-Palin voters as well. Romney might also have to contend with being overshadowed by his running mate — hardly something a presidential candidate wants to deal with.