Day of reckoning for Romney as Michigan votes

US Republican presidential candidate Mitt Romney accused rival Rick Santorum of trying to "kidnap" Michigan's Republican presidential contest on Tuesday as he faced the possibility of a humiliating defeat in the Rust Belt state where he grew up.

As Michigan voters cast their ballots, opinion polls showed Romney struggling to hold off Santorum in a state he had been expected to win easily a few weeks ago. Members of both parties can vote in the Republican primary, and Santorum has been appealing to the state's Democrats for support.

In an automated "robocall," Santorum criticized Romney, a wealthy former private equity executive, for opposing the 2008-2009 government rescue of the Detroit-based US auto industry while backing a Wall Street bailout.

"That was a slap in the face of every Michigan worker and we're not going to let Romney get away with it," the call said.

Santorum opposed both the auto bailout and the Wall Street bailout.

Romney said the robocall helps make the race unpredictable.

"There's a real effort to kidnap our primary process, and if we want Republicans to nominate the Republican who takes on Barack Obama, I need Republicans to get out and vote and say no to the dirty tricks of a desperate campaign," he told a news conference at his state headquarters in Livonia.

The stakes are particularly high for Romney in Michigan, where he was born and raised and where his father was a popular governor in the 1960s.

A defeat would raise more questions about the one-time front-runner's ability to appeal to conservatives and blue-collar voters in the state-by-state battle to take on Obama in the Nov. 6 general election.

Aides said Romney has the funds and organization to win his party's nomination even if he loses Michigan.

But a Santorum win, on the heels of his victories earlier this month in Colorado, Minnesota and Missouri, could upend the race. Republican Party leaders, concerned that Santorum's religious conservatism could make him unelectable against Obama, may feel pressured to search for a new candidate to join the race.

No matter what the outcome, Romney will likely end the evening with a greater lead over his rivals in securing the 1,144 delegates needed to win the nomination. He is expected to win handily in Arizona's winner-take-all contest, also taking place on Tuesday. Michigan awards its delegates on a proportional basis.

Until recent weeks, Santorum had trailed far behind Romney and several other Republicans vying for the nomination.

But other contenders have faltered, and the former Pennsylvania senator has leaped to the top of the pack, despite a skeletal campaign staff and a fundraising disadvantage.

When asked if he would win on Tuesday during a stop at his Grand Rapids headquarters, Santorum shrugged and quipped: "I'm not a pollster. We don't even have a pollster."

In Michigan, Santorum has stressed his own conservative views on social issues and criticized Romney as a moderate.

"He is a lightweight on conservative accomplishments," Santorum said at a news conference.

An ABC News/Washington Post poll found Romney at a new low among the most conservative US citizens. He is viewed favorably by just 38 percent of that group, the poll showed, down 14 points from a week earlier, while 60 percent view Santorum positively.