Rep. Michele Bachmann continues her startling rise in the polls, showing that she could be a serious threat to former Massachusetts Gov. Mitt Romney to be the frontrunner for the 2012 Republican presidential nomination.

The freshest evidence came in the form of a new Mason-Dixon poll published this week that showed her leading among likely GOP caucus-goers who will kick off the nominating process next winter.

The poll found Bachmann supported by 32 percent of those polled, a statistically insignificant lead over Romney's 29 percent -- scant weeks after she entered the race and many months after Romney launched his bid.

Former Gov. Tim Pawlenty came in third, with 7 percent support -- not great, but considerably better than the 2-3 percent range he has recently been polling.

In a head-to-head faceoff between Bachmann and President Obama, it's a tossup. Forty-seven percent of likely voters in the state would vote for Obama, while 46 percent would vote for the Sixth District congresswoman.

The poll, conducted last week, interviewed 629 likely voters in Iowa, 300 of them likely to take part in next winter's party caucuses. The margin of samling error of the entire sample is 3.9 percentage points; the margin for caucusgoers is 5.7 percent.

The poll was conducted a month before the symbolically important Republican straw poll held in Ames, which has turbocharged (or wrecked) the party's presidential aspirants. Romney is skipping the straw poll, while both Bachmann and Pawlenty have been incessantly stumping the state.