Detroit native Mitt Romney greets supporters with wife Ann in Novi, Mich., after squeaking out a win in Tuesday's primary. He also won Arizona.
Rick Santorum speaks at an election night rally in Grand Rapids, Mich., after he placed second in both Michigan and Arizona.
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Ron Paul drew large crowds in Springfield, Va., while finishing third and fourth in Michigan and Arizona. Virginia's primary is March 6.
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Romney supporters cheer during a primary night gathering at the Suburban Collections Showplace in Novi, Mich.
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Volunteer Vicki Groff points voters to the polls in Phoenix. Romney won 47.3 percent of the vote in Arizona; Santorum got 26.6.
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Santorum greets diners at New Beginnings Restaurant in Kentwood, Mich. He lost Tuesday but is atop polls in several states with March 6 primaries.
John Vandermark wears an "I Voted" sticker after voting in the Michigan primary at Royal Oak Farmers Market, in Royal Oak.
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Surrounded by children, Mitt Romney speaks to the media after a visit to his Michigan campaign headquarters in Livonia.
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A Republican voter goes to the polls at the Wickenburg Community Center in Wickenburg, Ariz., on Tuesday.
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Arizona Gov. Jan Brewer, who endorsed Mitt Romney in February, cast her vote for the former Massachusetts governor in Glendale.
Newt Gingrich supporters attend a campaign stop in Dalton, Ga. Gingrich skipped Michigan and Arizona to visit his home state, which votes March 6.
Gingrich and wife Callista meet Kaylan Cape, 5, in Dalton. The former Georgia congressman said Tuesday that he "unequivocally" has to win there.
Mitt Romney won both states that held primaries on Tuesday. But his margin in his home state of Michigan appears narrow enough to keep the GOP nominating contest lively for some time to come.
NPR projected wins for the former Massachusetts governor in both Arizona, where he won comfortably, and in Michigan, where he led Rick Santorum, 41 to 38 percent, with 99 percent of precincts counted.
It may be only a narrow win: Despite Romney's statewide victory, Michigan's delegate allocation could be split fairly evenly between the two top candidates. But it's good enough to deny Santorum bragging rights and prevent deep anxiety that would have been felt among Republicans had Romney failed to carry his home state.
"We didn't win by a lot, but we won by enough, and that's all that counts," Romney told supporters Tuesday.
"It's still a win, first of all," said Michigan Republican Rep. Bill Huizenga, a Romney supporter. "The bottom line is that Mitt still prevailed when Rick was extremely aggressive, including inviting Democrats to come into the primary and vote for him."
But Romney hasn't yet managed to seal the deal and become the certain nominee for the Republican Party.
If Romney had lost Michigan, the dominant narrative of the campaign would have been about his candidacy being on the ropes, said Henry Olsen, vice president of the American Enterprise Institute, a conservative think tank.
But such a narrow victory does not "re-establish the narrative of Romney as front-runner," Olsen said. "It means we now have the two-person race we've been looking for."
More Cliffhangers To Come?
For months, Romney has acted like the hero of an old movie serial. Facing one political near-death experience after another, he has always emerged to fight another day — only to face fresh danger around the next corner.
"There's been constant peril and constant adversity," said Scott Hagerstrom, Michigan state director for Americans for Prosperity, an advocacy group associated with the Tea Party. "Going into Super Tuesday" — the cluster of 10 primaries and caucuses next week — "that will be another test for Mitt Romney."
Over the next couple of weeks, many of the caucus and primary states look likely to favor Santorum, a former Pennsylvania senator and the more conservative candidate.
At this point, Santorum is the favorite in Tennessee and Oklahoma, which vote March 6, as well as Alabama and Mississippi, which vote on March 13.
"Certainly the short-term calendar — the next month — does bode relatively well for Santorum," said Corwin Smidt, a political scientist at Calvin College in western Michigan.
Romney will be favored in next Tuesday's contests in New England and the Mountain West. And, although Santorum may prevail in some of the Southern states to come, the key contest may well be in Ohio, which is voting next Tuesday.
"Ohio very slightly projects to be better for Santorum than Michigan," Olsen said, owing to demographic differences and the fact that Romney can't count on any home-state advantage there.
Listen to NPR's live special coverage of the Michigan and Arizona primaries.
Romney campaigned aggressively in Michigan, where his father, George, was governor during the 1960s.
"Romney had completely obliterated that big polling gap from 10 days to two weeks ago," when Santorum was ahead, said Bill Ballenger, editor of Inside Michigan Politics.
Gingrich and Texas Rep. Ron Paul, the two other remaining major GOP candidates, largely bypassed Michigan to concentrate on contests next month.
But new GOP rules for this election year block most states from giving all of their delegates to the statewide winner. That will keep Romney — despite having prevailed in all but one primary state to award delegates so far — from being able to put the game away.
"What this means is that nobody can really lock it up probably until June, so this constant bickering back and forth is going to continue all spring," said Mike Hellon, a former member of the Republican National Committee from Arizona.
"That was a bad political miscalculation," Hellon said of the new rules. "We are not going to have the opportunity for one or the other to emerge as the nominee presumptive and be able to attack [President] Obama."
How Romney Won
Reeling after Santorum's three-state sweep on Feb. 7, Romney appeared to regain his footing at a nationally televised debate last week in Arizona, when he managed to put Santorum on the defensive about his record in the Senate.
Romney and the superPAC supporting his bid have portrayed Santorum as a political insider who spent taxpayer dollars heavily through earmarks and supported controversial legislation as part of the compromised and compromising culture of Washington.
But Santorum may well have more staying power than the other candidates who have briefly emerged as Romney's chief rival, only to see their chances quickly implode.
"Santorum will be someone who stuck with him in his home state," said AEI's Olsen. "He'll be the first challenger to take the hit from Romney and not be obliterated."
It's a point Santorum stressed Tuesday night, even in conceding a Michigan victory to Romney. "A month ago, they didn't know who we are, but they do now," Santorum told supporters in Grand Rapids, Mich.
In contrast to earlier states, Romney wasn't able to swamp his main opponent by massively outspending him. The Romney campaign and its attendant superPAC may have outspent Gingrich by a 10-to-1 margin ahead of the Florida primary in January, but in Michigan his advantage was more in the neighborhood of 2 or 3 to 1, Ballenger said.
One question that has consumed the media for the past couple of days is how much of Santorum's Michigan support is owed to Democrats meddling in the process.
"When you've got Mark Brewer, the head of the Democratic Party in Michigan, calling on Democrats to vote in the Republican primary, I'm not sure he's appealing to that Macomb County Reagan Democrat," said Huizenga.
Santorum's campaign encouraged Democrats to cast a vote in the open GOP primary in protest against Romney's opposition to the federal bailout of the auto industry (which Santorum also opposed). Romney decried the tactic as a dirty trick.
Exit polls indicated that the number of self-identifying Democrats was up from past presidential years — but only slightly.
"In a close election, they might well have cost Romney a larger victory," said Smidt, of Calvin College.