Romney, 65, is clinching the presidential nomination later in the calendar than any recent Republican candidate — but not quite as late as Obama in 2008. Obama clinched the Democratic nomination on June 3, 2008, at the end of an epic primary battle with Hillary Rodham Clinton. Four years ago, John McCain reached the threshold on March 4, after Romney had dropped out of the race about a month earlier.
This year's primary fight was extended by a back-loaded primary calendar, new GOP rules that generally awarded fewer delegates for winning a state and a Republican electorate that built up several other candidates before settling on Romney.
Rick Perry, Herman Cain, Newt Gingrich, Rick Santorum and Trump — all of them sat atop the Republican field at some point. But Romney outlasted them all, even as some GOP voters and tea party backers questioned his conservative credentials.
The primary race started in January with Santorum, the former Pennsylvania senator, narrowly edging Romney in the Iowa caucuses. Romney rebounded with a big win in New Hampshire before Gingrich, the former House speaker, won South Carolina.
Romney responded with a barrage of negative ads against Gingrich in Florida and got a much-needed 14-point win. Romney's opponents fought back: Gingrich called him a liar, and Santorum said Romney was "the worst Republican in the country" to run against Obama.
Gingrich and Santorum assailed Romney's work at Bain Capital, the private equity firm he co-founded, saying the firm sometimes made millions at the expense of workers and jobs. It is a line of attack that Obama has promised to carry all the way to November.
On Feb. 7 Santorum swept all three contests in Missouri, Colorado and Minnesota, raising questions about Romney's status as the front-runner. After a 17-day break in the voting, Romney responded with wins in Arizona, Michigan and Washington state before essentially locking up the nomination on March 6, this year's version of Super Tuesday.
Romney has been in general-election mode for weeks, raising money and focusing on Obama, largely ignoring the primaries since his competitors dropped out or stopped campaigning. Santorum suspended his campaign April 10, and Gingrich left the race a few weeks later.
Both initially offered tepid endorsements of Romney, but on Sunday Gingrich gave a full-throated defense of Romney's campaign, saying on NBC's "Meet the Press" that he was "totally committed to Romney's election."
Texas Rep. Ron Paul said on May 14 he would no longer compete in primaries, though his supporters are still working to gain national delegates at state conventions.
Rich Galen, a Republican strategist who has been unaligned in the 2012 race, said the long, sometimes nasty primary fight should help Romney fine-tune his campaign organization so it can operate effectively in the general election. Galen doesn't, however, think it was relevant in toughening up Romney for the battle against Obama.
"Romney's been running for president for six years. He is as good a candidate as he's ever going to be," Galen said. "Whatever you say about him, he was better than everybody else in the race."
Associated Press writer Steve Peoples contributed to this report from Colorado.
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