Mitt Romney is fighting to avoid an embarrassing home-state loss in a high-stakes Michigan primary that will not decide the Republican presidential contest but could scar the former Massachusetts just a week before Super Tuesday.
Rival Rick Santorum is calling upon an unusual coalition of tea party activists, religious conservatives and Democrats to help topple Romney and reclaim the momentum in the increasingly heated nomination battle.
Santorum, a former Pennsylvania senator, confirmed on the eve of the election that he had targeted Michigan Democrats with automated phone calls encouraging them to vote against Romney.
"Romney supported the bailouts for his Wall Street billionaire buddies but opposed the auto bailouts," the phone call said. "That was a slap in the face to every Michigan worker and we're not going to let Romney get away with it."
Only declared Republicans may vote in Tuesday's GOP primary, but party rules allow voters to change their affiliation temporarily on the spot. The potential involvement of Democrats adds a new twist to a contest already expected to have significant implications for Romney's White House bid.
Neither Newt Gingrich nor Ron Paul is actively competing in Michigan's contest, or in Arizona's Tuesday primary, which Romney is expected to win handily, in part because of the state's Mormon population.
Romney was born and raised in Michigan, where his father served as governor. But Santorum's rise in polls following a three-state sweep earlier in the month has forced Romney to work hard in Michigan over the past week. He's hosted nearly a dozen public events as he and his allies have spent more than $2 million on local television advertising.
Santorum will campaign Tuesday around Grand Rapids, a city set in a western Michigan region home to many social conservatives and tea party supporters. Romney is set to meet with voters 130 miles to the east in suburban Detroit, an area with a larger collection of moderate Republicans, a key segment of his support.
Romney's overwhelming advantages in Michigan, however, may not pay off in a contest generally dominated by the Republican Party's more conservative flank. He trailed Santorum by a significant margin in polls as recently as last week. In recent days, however, those polls have tightened, leaving Tuesday's election essentially a tossup.
Romney predicted victory Monday night as a crowd gathered at the Royal Oak Music Theatre waited to hear rocker-rapper Kid Rock perform.
"I'm going to win in Michigan and I'm going to win across the country," Romney said.
Santorum, perhaps in a nod to the recent swing in the polls, was more cautious as he spoke to voters in Lansing.
"I think the fact that we are doing as well as we are is a pretty big deal in this state," he said.
Paul, who was ending a three-state tour of Michigan on Monday, told supporters that his goal is to "whittle away" at the total number of delegates available. Speaking to supporters in Democrat-friendly Detroit, the Texas congressman said, "Everybody knows I'm not a conventional Republican."
No matter the top finisher, Romney and Santorum stand to split the 30 delegates at stake because Michigan distributes delegates proportionally. By contrast, Romney is favored to capture all 29 delegates in Arizona, which features a winner-take-all system.
Washington state holds its caucuses Saturday, with 40 delegates at stake. On Super Tuesday, March 6, 10 primaries and caucuses take place, with 419 delegates.
Romney has 123 delegates to 72 for Santorum, 32 for Gingrich and 19 for Paul in the Associated Press count, with 1,144 required to win the party nomination at the Republican National Convention in Tampa, Fla.