FOREST LAKE, Minn.—A year ago, Michele Bachmann was fighting for the GOP presidential nomination. Now she's battling to hang on to her House seat.

The Minnesota congresswoman, who rode a wave of tea-party support to national prominence last year before her campaign fizzled out, is now trying to fend off Democratic rival Jim Graves, a multimillionaire hotel developer. Mr. Graves has accused Ms. Bachmann of being more in tune with the hard-line conservatives who supported her presidential bid than most of the voters back home in their Republican-leaning district.

Recent polling shows that Ms. Bachmann, who won her congressional seat by 13 percentage points two years ago, has seen her popularity erode in Minnesota's Sixth Congressional District, which sits just north of Minneapolis. A poll of 1,000 likely voters last week commissioned by the Star Tribune newspaper showed Ms. Bachmann leading Mr. Graves 51% to 45%, within the poll's margin of error of plus or minus three percentage points. The remaining 4% were undecided. The candidates' three planned debates all are scheduled for the week before the vote, which could help keep the race close down to the wire.

Ms. Bachmann's social-conservative roots helped her win the Iowa straw poll in August of last year and earned her comparisons to Sarah Palin, the 2008 GOP vice-presidential nominee. But her presidential campaign faltered afterward as the field became more crowded, and she dropped out after the Iowa caucuses in January.

This election season, Ms. Bachmann is part of a small group of outspoken GOP House members aligned with the tea-party movement who face tough races, in part because Democrats have targeted them. Still, political handicappers predict that most of the 60 members of the House's tea-party caucus, which Ms. Bachmann heads, will win re-election. Others facing tough fights include Reps. Steve King of Iowa, Allen West of Florida and Joe Walsh of Illinois.