WASHINGTON — Republican presidential rivals Mitt Romney and Rick Santorum collided Tuesday in a rancorous Michigan primary that tested the clout of the GOP establishment against conservative and tea party rebels as well as the candidates themselves.
Arizona Republicans voted in the second primary of the night, and Romney was favored by far in that race that drew scant attention.
As Romney's home state, Michigan held outsized importance in the campaign to pick a Republican presidential candidate, a place where he won the primary in 2008 and could ill afford to lose this year.
Not even the opening of polls around the state brought an end to the squabbling. Romney accused Santorum of trying to hijack a victory by courting Democratic votes through automated telephone calls and suggested his rival was appealing to Michigan conservatives by making the kind of "incendiary" statements he would not.
"I'm not willing to light my hair on fire to try and get support," Romney said. "I am what I am."
Santorum brushed aside the allegations of hijacking, saying Romney had appealed for support from independents in earlier states.
"We're going to get voters that we need to be able to win this election. And we're going to do that here in Michigan today," Santorum said, referring to blue collar voters with a history of swinging between the parties.
If nothing else, the unexpected clash on Romney's home field dramatized that two months into the campaign season — after nearly a dozen primaries and caucuses — the GOP race to pick an opponent for President Barack Obama was as unsettled as the day it began.
Two other candidates in the race, Newt Gingrich and Ron Paul, made little effort in either Michigan or Arizona, pointing instead to next week's 10-state collection of Super Tuesday primaries and caucuses.
Michigan loomed as a key test for Romney as he struggled to reclaim his early standing as front-runner in the race. The first of the industrial battleground states to vote in the nominating campaign, it is also the place where the former Massachusetts governor was born and where he won a primary when he first ran for the party nomination four years ago.
But Santorum, a former Pennsylvania senator, rolled into the state on the strength of surprising victories on Feb. 7 in caucuses in Minnesota and Colorado plus a non-binding primary in Missouri. He quickly sought to stitch together the same coalition of conservatives and tea party activists that carried him to a narrow victory in the Iowa caucuses that opened the campaign nearly two months ago.
The Michigan primary was open to Republicans or any voter who declared they were Republican for the purpose of voting, and there was precedent for an influx of outsiders influencing the outcome.
A dozen years ago, John McCain defeated the heavily favored George W. Bush, relying on the support of Michigan independents and Democrats. Exit polls then showed that Bush won 66 percent of Republican votes, while McCain won 82 percent of self-described Democrats and 67 percent of independents. Together, the non-Republican voters accounted for more than half the electorate.
In a measure this year of the state's importance to the battle for the nomination, the two leading candidates and the super PACs that support them spent about $6 million on television advertisements, and Romney and Santorum spent much of the past 10 days crisscrossing the state in search of support.
Arizona was Romney's to lose, judging by the behavior of his rivals, who spent little time campaigning in the state and no money advertising on its television airwaves.
In all, there were 59 delegates at stake in the two states.
Arizona awarded all 29 of its delegates to the winner of the statewide vote.
In Michigan, by contrast, 30 delegates were apportioned according to the popular vote. Two were set aside for the winner of each of the state's 14 congressional districts. The remaining two delegates were likely to be divided between the top finishers in the statewide vote.
Romney entered the night the delegate leader in The Associated Press count.
He had 123, compared to 72 for Santorum, 32 for Gingrich and 19 for Paul. It takes 1,144 to win the nomination at the Republican National Convention in Tampa next summer.
There are 40 delegates at stake in Washington caucuses on Saturday, followed by 419 on Super Tuesday.
Santorum campaigned heavily for the support of tea party activists and other non-establishment Republicans, appearing in churches at times and often dwelling on social issues, as is his custom. In a string of attention-gathering remarks in the race's final days, he said Obama was a snob who wanted everyone to attend college, said he nearly threw up over a speech that candidate John F. Kennedy gave in 1960 about the separation of church and state, and said Romney was uniquely unqualified to defeat Obama because the two men shared so much in common on issues like health care.
The former Massachusetts governor made a play for tea party support, too, at a pair of appearances, but for the most part campaigned on his pledge to use his background as a successful businessman to help create jobs and fix the economy. Last week, he issued a call for 20 percent across-the-board cuts in personal income tax rates.
But he was hampered by off-the-cuff comments that reinforced his difficulty in reaching out to struggling voters in a state with 9.3 percent unemployment. He said at one point that his wife drives a couple of Cadillacs, and at another that he was friends with some of the owners of NASCAR teams.
At a rare news conference after the polls opened on Tuesday, he conceded that his own mistakes had hurt his campaign.
The primaries in Michigan and Arizona were the first contests since Romney squeaked out a victory over Paul in the Maine caucuses on Feb. 11, a lull of two and a half weeks.
Except for a debate in Arizona last Wednesday and a brief burst of campaigning in the hours before and after, Romney and Santorum have focused their time and campaign money on Michigan.
Polls showed Santorum racing to a large advantage after his victories on Feb. 7, before the weight of attack ads by a Romney-aligned super PAC and the candidate himself began to narrow and finally erase the gap in many surveys.
In the end, the combination of Romney and the outside group accounted for about $3.8 million in TV ads, compared to about $2.2 million for Santorum and a super PAC supporting him.
While that gave Romney an advantage, it wasn't nearly as lopsided as in some of the earlier states.
Kasie Hunt reported from Michigan.