Romney slipping in key, boyhood state of Mich.

The next big contest in the battle for the Republican presidential nomination is the Michigan primary at the end of the month.

Rick Santorum is surging there, and has taken the lead over Mitt Romney in several national polls.

As Romney campaigns in Michigan, he's calling himself the underdog.

Michigan could be make-or-break for him. He grew up there. His father was the governor. Until recently, his campaign was hoping for an easy win. Not anymore.

Romney threw himself a "welcome home" rally Wednesday night in Grand Rapids. "There are a lot of high-schoolers here," he said. "I'm just, it really does bring back memories."

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As his campaign in the critical state shifted into high gear, he seemed to acknowledge he has ground to make up, telling a reporter, "It's always a good thing to be seen as the underdog, to be fighting hard. Never take anything for granted. Work very hard"

Romney hopes a victory in Michigan will help him regain the momentum he lost last week, when Santorum won three states, changing the dynamic of the race.

In Michigan, which has an unemployment rate over 9 percent, Santorum is highlighting his plan to revitalize manufacturing.

Several new polls have Santorum ahead of Romney in Michigan, one of them by six points.

That has the ad war heating up, with Romney reminding voters it's his home turf. One ad says, "Michigan's been my home, and this is personal."

And a Super PAC supporting his candidacy has already committed more than $600,000 to try to do to Santorum what it did to Newt Gingrich in Florida. One ad calls Santorum a "big spender" and "Washington insider." The anti-Gingrich ads reminded voters Gingrich has "more baggage than the airlines."

Santorum is fighting back with a new ad of his own, complete with a Romney lookalike firing mud at a Santorum cutout. "In the end," says the ad, "Mitt Romney's ugly attacks are going to backfire."

Santorum is speaking to the Detroit Economic Club Thursday to lay out his manufacturing plan.

Romney gets an important endorsement Thursday, from Mich. Gov. Rick Snyder.

To see Chip Reid's report, click on the video in the player above. CBS News political director John Dickerson told "CBS This Morning" co-hosts Charlie Rose and Erica Hill there's plenty on the line for Romney in Michigan, where he's "put all his chips." For more of Dickerson's analysis, click on the video below.

  • Chip Reid

    Chip Reid is CBS News' national correspondent.