WASHINGTON — Michele Bachmann, a tea party firebrand and 2012 presidential contender, announced on Wednesday she will not seek re-election to the U.S. House of Representatives but said her surprise decision had nothing to do with multiple investigations into her campaign finances.

Bachmann, a conservative Minnesota Republican whose outspoken style and sharp criticism of President Barack Obama made her a prominent and polarizing national figure, did not give a specific reason for stepping down. But she said she was not ducking the likelihood of a difficult re-election fight in her suburban Minneapolis district.

Bachmann, 57, faced a probable rematch next year with Democrat Jim Graves, who came within 1 percentage point of beating her in 2012 in a congressional district that was carried easily by Republican presidential contender Mitt Romney.

“My decision was not influenced by any concerns about my being re-elected,” Bachmann said in an 8 1/2 minute video announcement posted on her campaign website in which she sat in front of a bookcase and spoke over light rock music reminiscent of political ads.

Bachmann also said the decision was “not impacted in any way by the recent inquiries” into her 2012 White House campaign, which is the subject of at least five federal and state investigations into potential campaign finance violations.

The Federal Election Commission, the Federal Bureau of Investigation, the Office of Congressional Ethics, the Iowa Senate Ethics Committee and a local Iowa police department are looking into allegations about the campaign.

A former Bachmann staffer has alleged that an Iowa state senator who was chairman of Bachmann’s campaign received third-party payments for his work from another company in order to sidestep Iowa Senate ethics rules.

Another allegation involves the possible theft and misuse of an email distribution list maintained by an Iowa home-school group. As a candidate, Bachmann courted voters involved in the home-schooling movement.

The investigations are not likely to be affected by the announcement by Bachmann, who will serve in Congress until January 2015. An Iowa Supreme Court justice appointed a special investigator to look into the allegations.

“It was clearly understood that compliance with all rules and regulations was an absolute necessity for my presidential campaign, and I have no reason to believe that that was not the case,” Bachmann said in the video.

Bachmann’s decision to retire probably will make it easier for Republicans to hold the seat in a heavily Republican district that Romney won by 15 percentage points in 2012.

“She was still favored for re-election to Congress by virtue of her district being so Republican, but all of those problems she faced had to be physically and mentally taxing,” Minnesota Republican strategist Ben Golnik said.

Her retirement completes a stunning fall for Bachmann, whose penchant for inflammatory rhetoric shot her to national prominence and made her an early favorite of the tea party movement.

Bachmann’s presidential bid got off to a quick start in 2011 when she won the Iowa straw poll, seen as a traditional test of strength in the state that kicks off the presidential nominating contest. But Texas Gov. Rick Perry entered the Republican race on the same day, and he quickly soaked up much of her conservative support.

Bachmann’s campaign faded quickly; she finished a distant sixth in the Iowa caucus vote in January 2012, prompting her to drop out of the race the next day.

She remained a prominent conservative voice, however, although one known for inflammatory and sometimes inaccurate takes on national issues.

While she helped elevate opposition to Obama’s health care overhaul to a touchstone issue for Republicans, she often was mocked during the presidential campaign for her outrageous or incorrect statements.

She confused the late actor John Wayne with serial killer John Wayne Gacy, praised the Founding Fathers for ending slavery — which actually ended nearly a century after the nation was founded — and suggested that a crowd sing “Happy Birthday” to the late singer Elvis Presley on the anniversary of his death.

More seriously, she suggested that a vaccine for a virus linked to cervical cancer led to “retardation,” and last year was criticized for accusing Huma Abedin, an adviser to then-Secretary of State Hillary Clinton, of having ties to the Muslim Brotherhood, a conservative Islamist group.

Her decision not to seek a fifth two-year term in Congress came as a shock to Republicans in her district, who said she had shown no signs that she would not run. Bachmann aired her first campaign commercial this month, earlier than usual for a House campaign and a sign that she had not been planning her retirement for long.

“I fully expected her to run again and to win again,” Minnesota Republican Party Chairman Keith Downey said.

Democrats were quick to pounce on Bachmann’s announcement, sending out a fundraising appeal within hours touting her “crazy” Web video and proclaiming that Republicans were wondering “who’s next to go.”

In her video, Bachmann thanked her husband, five children and 23 foster children and said she would dedicate the rest of her congressional term to fighting for “traditional marriage, family values, religious liberty and academic excellence.”

She did not rule out a future run for public office, but analysts suggested that conservative talk radio or television talk shows were a more likely avenue for her future.

“She stirs the pot like few politicians do. There are ways to make a lot of money and have a career without running for public office again,” said political scientist Steven Schier of Carleton College in Minnesota.

“When you are flamboyant, divisive and controversial, you limit your appeal with the broader electorate,” he said. “That’s the lesson of Michele Bachmann’s career.”