But the poll's revelation of slipping enthusiasm for the president could worry his reelection staff in Chicago. Earlier this week, the Obama campaign ranked Michigan and its 16 electoral votes as "lean Democratic" in a Web video assessing the state of the campaign and urging supporters to be optimistic.

Yet only 46 percent of Michiganders surveyed say they have a favorable opinion of the president, and four in 10 approve of the job he's doing. That's down from earlier in the year, and below national averages, despite the president's auto bailout remaining extremely popular in the state.

In fact, more than twice as many Michigan voters surveyed said Romney's position on federal aid to automakers would make them less likely to support his candidacy than likely to vote for him in November. Romney is also considered unfavorable by more voters, at 43 percent, than those who view him favorably, at 41 percent.