WATERLOO, Iowa - Congresswoman Michelle Bachmann kicked off her presidential campaign in Iowa, where a strong finish in the state's early nominating caucus could position the anti-tax tea party candidate as a serious challenger to more mainstream Republicans hoping to take on President Barack Obama in 2012.

An outspoken three-term congresswoman from neighbouring Minnesota, Bachmann made the announcement Monday in her birthplace of Waterloo. Iowa holds the first Republican nominating contest, conducted through meetings known as caucuses.

The Midwestern state is important for Bachmann: Her popularity among Christian conservatives and tea party activists -- she created the Tea Party Caucus in Congress -- make her a natural fit for the caucus electorate. Iowa could pave the way for strong showings in other nominating contests.

A Des Moines Register's Iowa poll released Saturday showed Bachmann in a statistical tie with perceived Republican front-runner former Massachusetts Gov. Mitt Romney, among likely caucus-goers. Romney hopes to draw on the same hometown relationship in New Hampshire during that state's party primary election that Bachmann has in Iowa.

Republican voters could shy away from Bachmann if they are more concerned about choosing the most electable candidate in a position to defeat Obama. But she rejected questions about whether she can reach beyond the Republican base to appeal to the moderate independent voters needed to defeat Obama in November 2012.

"The liberals, and to be clear I am not one of those, want you to believe the tea party movement is just the right wing of the Republican Party," she said. "Nothing could be further from the truth."

Bachmann is known for piercing commentary that has endeared her to some voters, but at times her inaccurate commentary has led others to label her as a fringe candidate. She once falsely complained that taxpayers would be stuck with a $200 million per day tab for an Obama trip to India and accused the first black U.S. president of running a "gangster government."

"Her trick is going to be to maintain that boldness and to somehow rein it in and discipline it so it works for her and not against her," said Republican pollster Mike McKenna, who isn't working for any 2012 presidential candidates.

In Congress, Bachmann became known for trying to block Obama's health care law, which she is now promising to repeal. She has also tangled with Republican leaders in the House of Representatives over her concerns they are too timid on federal spending cuts.

Her unswerving style provides a sharp contrast with more measured Republican rivals, including Romney, Tim Pawlenty and Jon Huntsman and former House Speaker Newt Gingrich. Others vying for the nomination are ex-Sen. Rick Santorum, Texas Rep. Ron Paul and businessman Herman Cain.

Bachmann is the only woman in the race so far, and she is often compared to fellow Republican Party maverick and tea party favourite Sarah Palin, the Republican's 2008 vice-presidential candidate. Palin has not said whether she intends to run in 2012.

Romney, who sought his party's presidential nomination in 2008, already faces questions from Bachmann and other rivals about his record of changing positions on social issues including abortion and gay rights, shifts that have left conservatives questioning his sincerity. In addition, Romney championed a health care law enacted in Massachusetts that is similar to Obama's national health overhaul, which Republicans oppose.