Evan Vucci, Associated Press
In this Oct. 1, 2009, file photo, Rep. Alan Grayson, D-Fla., listens during a hearing on Capitol Hill in Washington.

TALLAHASSEE, Fla. — Democratic Congressman Alan Grayson announced Thursday he will seek the Senate seat Republican Marco Rubio is leaving to run for president, dismissing the idea that he is too liberal to win a statewide election in Florida.

The decision guarantees a feisty primary between the unabashed liberal and U.S. Rep. Patrick Murphy, a former Republican who is running as a moderate and who has garnered the support of many party leaders. Grayson, who represents a central Florida district, made his announcement on Orlando television station WKMG.

Grayson, 57, is a wealthy lawyer who's proud of being non-establishment. He calls himself a congressman with guts who answers to no one but voters. While his headline-making comments will certainly be discussed in during the campaign — as well as his messy divorce and some ethical questions about hedge funds — Grayson says his record of accomplishment and not his rhetoric will be what's measured in the election.

"I am the most productive member of Congress. Time magazine referred to me as a standup congressman in a do-nothing Congress," Grayson said in a telephone interview.

And despite previously calling Republicans the White Christian Party that has a platform of hate and fear, he said no one else has been more successful at working across political aisles to pass good legislation.

Grayson also said Democrats won't support Murphy, who once donated money to Mitt Romney and who is running as a moderate. Grayson predicted he would win the primary with the support of every major segment of his party.

"The black vote, the Hispanic vote, the Jewish vote, the gay vote, the liberal vote, the labor vote — these are all blocs that have seen me accomplish concrete things to the benefit of those groups. These are my supporters," Grayson said. "I suppose that Patrick has the support of all the Democrats who gave $2,300 to Mitt Romney, because he's one of them."

Murphy issued a statement shortly after Grayson's announcement.

"I look forward to a clean, honest discussion of the issues in this primary. I have built a strong record of working together to get things done, while remaining true to core Democratic principles," he said.

Don't expect party leaders to suddenly change their thinking that Murphy is the better general election candidate in a state that is politically more toward the middle, having elected a Republican governor five straight elections but supported President Barack Obama twice.

"Grayson has a following, he will work the progressive wing of the party very hard, but in the end I think Murphy will be more formidable candidate," said Rod Smith, a former state Democratic Party chairman who sought the Democratic nomination as a moderate in 2006. "If we're going to win the general election, Murphy is the more likely candidate."

Republican U.S. Rep. Ron DeSantis has already announced he's running for the GOP nomination, as has little-known businessman and veteran Todd Wilcox. Lt. Gov. Carlos Lopez-Cantera is expected to enter the race next week and Republican U.S. Rep. Jeff Miller is strongly considering a run.

As Grayson enters the race, he has a stronger social media following than Murphy. Here are the numbers as Grayson prepared to make his announcement:

— Facebook: Grayson, 127,458 likes; Murphy, 31,350 likes.

— Twitter: Grayson, 59,646 followers; Murphy, 4,174 followers.

— YouTube: Grayson, 11,175 subscribers and 10,756,712 views; Murphy, a combined 155 subscribers and 51,080 views between his congressional and campaign accounts.

Both men are formidable fundraisers and Murphy has also proven he can win a tough fight against a partisan favorite, though in his case it was tea party star and then-Congressman Allen West who he ousted, not a fellow Democrat. He beat West in 2012 in a close race and easily won re-election last year in a slightly Republican-leaning district.

Murphy, 32, has already wrapped up the endorsement of the Democratic Senatorial Campaign Committee, as well as a long list of Florida legislators, mayors and members of Congress.

Grayson has scoffed at the support Murphy is receiving. Leading up to his announcement, Grayson posted on Facebook and Twitter a question asking voters who else in Congress can make this statement: "I am unbought and unbossed. I owe nothing to anyone but The People."

Follow Brendan Farrington on Twitter: http://twitter.com/bsfarrington .