Despite his trifecta of embarrassing defeats last week – losing to Rick Santorum in Colorado, Missouri, and Minnesota – Mitt Romney could look ahead to the upcoming primary schedule with some confidence. Michigan, on Feb. 28, should be his. He was born and raised there; in 2008, he won the Michigan primaries by 9 points.

Not so fast.

According to two new polls, Mr. Romney is now trailing Mr. Santorum in Michigan.

An American Research Group poll of likely Republican Voters has Santorum ahead of Romney 33 percent to 27 percent. (Newt Gingrich got 21 percent and Ron Paul 12 percent.)

And in another sign of Romney's "enthusiasm gap" problem, the most committed voters are the ones least likely to vote for him. Among voters who say they will definitely vote in the primary, Santorum leads Romney 36 percent to 25 percent. Among those who only say they'll "probably" vote, Romney comes out on top by 11 points.

Another poll, by Public Policy Polling, is even worse for Romney. It has Santorum leading Romney 39 percent to 24 percent. One critical factor in Santorum's surge ahead, according to PPP: Gingrich's nosedive. Increasingly, it looks like the "anti-Romney" Republicans are coalescing around Santorum as their candidate.

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Despite his relatively low support (Gingrich got 11 percent in the poll), his continued presence still benefits Romney. PPP's analysis:

"Republican voters aren't just declining to vote for Gingrich at this point – they don't even like him anymore. Just 38 percent have a favorable opinion of him to 47 percent with a negative one. His numbers are inching back closer to what they were before his surge in the polls began in November. His continued presence in the race is a boost to Romney though. 54 percent of his supporters would go to Santorum if he dropped out, compared to only 21 percent for Romney and 14 percent for Paul. Santorum's lead in a Newt-less field would expand to 21 points with him at 48 percent to 27 percent for Romney and 13 percent for Paul. So every day Gingrich stays in is a saving grace for Romney's hopes."

Other interesting tidbits from the PPP poll: People really like Santorum. (He gets a 67/23 breakdown on voters who view him favorably versus unfavorably, compared with 49/39 for Romney.) And despite the media discussion of Romney's home-state advantage in MIchigan, voters there don't agree. Only 26 percent of primary voters consider Romney to be a Michigander (62 percent do not).

In addition to the likeability factor, what else could be behind the shift? For one thing, Romney has repeatedly struggled in the Midwest – and Santorum's message (which includes reviving American manufacturing) may be a more natural sell to some of the blue-collar Republicans in a place like Michigan. (Romney, in contrast, has done better in wealthier counties around major cities.)

Just as in Colorado and Minnesota, which he won in 2008 and lost last week, Romney faces the challenge of no longer being the "conservative alternative" to the mainstream candidate as he was back then, but the mainstream candidate that conservatives are trying to beat.

Romney may also be regretting that stand he took against the auto bailouts back in 2008, when he wrote a New York Times op-ed that was given the unfortunate headline "Let Detroit Go Bankrupt."

In coming weeks, look for Romney to spend more time and money in Michigan. Arizona's vote, also held Feb. 28, at this point looks like more of a sure thing for Romney, but a defeat in either state would be a major blow.

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The best news for Romney in Monday's polls: Voters are still undecided. The PPP poll shows a majority of voters (53 percent) still open to changing their minds.

The Michigan vote is over two weeks away – and if there's anything this election has shown to date, it's that candidates' fortunes can swing wildly in a short amount of time. In Florida, polls showed massive shifts toward Gingrich in the days right after his South Carolina win, only to tilt back toward Romney in just over a week. In the end, of course, Romney won by 14 percent.