WASHINGTON — Mitt Romney collided with rivals Rick Santorum and Newt Gingrich on Tuesday in primaries in Alabama and Mississippi, hotly contested Southern crossroads in the struggle for the Republican presidential nomination.
Caucuses in Hawaii were also on the calendar in the race to pick an opponent to President Barack Obama this fall.
There were 107 Republican National Convention delegates at stake, 47 in Alabama, 37 in Mississippi, 17 in Hawaii and six more in caucuses in American Samoa.
Each of the three leading contenders faced a different challenge in Alabama and Mississippi, where heavy television advertising was evidence of the states' unaccustomed significance deep in the nominating campaign.
Gingrich struggled for political survival, Romney sought a strong showing to silence his critics and Santorum hoped to emerge at last as the chief conservative rival to the front-runner.
Rep. Ron Paul, the fourth contender, made little effort in the states on the day's ballot.
The Southern showdown came as new polling showed a recent decline in Obama's approval ratings — after they had been rising — amid escalating gasoline prices and turbulence in the Middle East. And those issues were showing up in the Republican campaign.
Romney, campaigning in St. Louis, said Tuesday that Obama has said gas prices are high because GOP presidential candidates are talking "in a very muscular way about Iran and their nuclear program." Obama said in an interview Monday that the biggest driver "of these high gas prices is speculation about possible war in the Middle East" and that his administration has been trying to reduce "some of the loose talk" about war.
In Alabama, Santorum picked up a vote from Gov. Robert Bentley, who had not publicly endorsed the former Pennsylvania senator. Bentley's spokesman said the governor traveled to his hometown of Tuscaloosa to vote for Santorum, whom he considers "the most conservative candidate in the Republican presidential race."
In Birmingham, Gingrich told reporters he felt "pretty good" about his chances Tuesday night.
With polls showing an unexpectedly tight race in the conservative bellwether states, Romney stopped in Alabama on Monday — a clear indication he was eyeing a potential win there.
Evangelical voters played an outsized role in both Alabama and Mississippi, underscoring the test for Romney, the former governor of Massachusetts. Four years ago, 77 percent of GOP primary voters in Alabama and 69 percent in Mississippi said they were born again or evangelicals.
Those voters have been reluctant to rally to Romney's side in the primaries and caucuses to date. His best showing in a heavily contested primary so far was 38 percent in Florida.
The day began with Romney leading the delegate competition by far in The Associated Press count, with 454 of the 1,144 needed to win the nomination. Santorum had 217, Gingrich 107 and Paul 47.
That gave the former Massachusetts governor more than his rivals combined. And while Santorum in particular challenges the mathematical projections, Romney is amassing delegates at a rate that puts him on track to clinch control of nomination before the convention next summer.
The large amount of television advertising was testimony to the importance the contenders and their allies attached to the primaries in both Alabama and Mississippi.
All three candidates as well as super PACs supporting each of them ran television commercials. As has been the case all year, Restore Our Future, which backs Romney, spent more than any of the others. The group put down $1.3 million for television ads in Alabama, another $900,000 in Mississippi and more for radio on Christian and other radio stations as well as thousands of pieces of mail designed to help the former Massachusetts governor.
It was only in recent days that Romney seemed to sense a chance in Alabama and Mississippi, and he responded by increasing his television ad expenditures and his plans for campaigning in the states.
Born in Michigan and a longtime resident of Massachusetts, he told one audience the two primaries were "a bit of an away game for him" and drew laughs from another when he said he hoped to go hunting with an Alabama friend "who can actually show me which end of the rifle to shoot."
He generally steered away from criticizing his Republican rivals and aimed his rhetoric instead at Obama, whose prospects in both states are as dim next fall as anywhere in the country.
Romney set his focus on amassing delegates as aides argued only he has a chance to gain the support needed to clinch the nomination by the time the party convention opens in August.
Santorum's camp issued a rebuttal on primary eve that said Romney's claims were based on fuzzy math. "Simply put, time is on our side," it said.
The former Pennsylvania senator campaigned against the president and Romney simultaneously as he sought the support of conservatives who have fueled his recent surge.
Campaigning in Biloxi, Miss., on Monday, he ridiculed the science behind global warming. "The dangers of carbon dioxide? Tell that to a plant, how dangerous carbon dioxide is," he said.
Gingrich spent part of his time pushing back against suggestions — including from his own staff — that he might drop out if he didn't notch a pair of Southern victories. His only two wins so far came in the South Carolina primary on Jan 21, and last week, when he won his political home state of Georgia.
Initial polls showed the former House speaker in a strong position in both states, but he abruptly canceled a campaign trip to Kansas in advance of the state's caucuses late last week to remain in the South.
He used a recorded telephone message from Chuck Norris, the actor and Karate champion, for a last-minute appeal to voters in Alabama.
Associated Press writers Charles Babington in St. Louis and Beth Fouhy and Philip Elliott in Montgomery, Ala., contributed to this report.