MARQUETTE, Mich. - Rep. Bart Stupak insists that tea party activists outraged over his crucial support of health care legislation didn't run him out of office, but his decision to retire gives conservatives a rallying point as they target Democrats in the midterm elections. The congressman, an anti-abortion Democrat whose high-profile role in the "Obamacare" debate earned him enemies on the left and the right, said Friday that he's leaving because he's tired and has accomplished his No. 1 goal: improving health care.

MARQUETTE, Mich. - Rep. Bart Stupak insists that tea party activists outraged over his crucial support of health care legislation didn't run him out of office, but his decision to retire gives conservatives a rallying point as they target Democrats in the midterm elections.

The congressman, an anti-abortion Democrat whose high-profile role in the "Obamacare" debate earned him enemies on the left and the right, said Friday that he's leaving because he's tired and has accomplished his No. 1 goal: improving health care.

"The tea party did not run me out," Stupak told The Associated Press in a phone interview. "If you know me and my personality, I would welcome the challenge."

Stupak had been a consistent landslide winner in his sprawling northern Michigan district, and the opening now offers Republicans a ripe opportunity to regain a seat they held for decades until Stupak prevailed in 1992.

His political foes - tea party activists and abortion opponents - both claimed credit for forcing him into retirement, and Michigan GOP Chairman Ron Weiser declared that the nine-term incumbent had become the first casualty of the battle over health care in Congress.

"Bart Stupak's decision to retire is emblematic of the many Democrats in swing districts who have been forced into casting tough votes in favor of politically unpopular policies at the behest of House Speaker Nancy Pelosi," added Ken Spain, communications director for the House Republican campaign committee.

No prominent or well-funded Republican, however, had stepped in to challenge Stupak, who said he was confident of winning re-election. The 58-year-old said he was withdrawing because he was worn out and wanted more family time after nearly 18 years in Congress and the grueling health care battle.

"I've struggled with this decision. I've wanted to leave a couple of times, but I always thought there was one more job to be done," he said at a news conference.

"Since the day I took office, I fought to improve the quality and accessibility of health care," he said. "My No. 1 legislative goal has been accomplished."

Stupak had little national profile before the health care debate. He led a group of anti-abortion Democrats who held out against the legislation until President Barack Obama agreed to sign an executive order ensuring that federal funds would not be used for abortions. That quickly transformed him from the bane of the bill's supporters to the bane of its foes.

As he announced his decision, Stupak mentioned threats he has received because of his stance on various issues, including health care.

"The three o'clock in the morning phone calls, that's people outside the district," he said. "That's not my district. I know these folks. They wouldn't do that. You sort of just ignore it and move on."

Stupak's retirement marked the latest in a series of political setbacks for a party striving to retain control of Congress against a backdrop of recession and high unemployment.

So far, 20 Democrats and 20 Republicans have either resigned or announced they will not run again in the fall, but the equal numbers mask a clear advantage for the GOP. Democrats will be defending at least a dozen potentially competitive open districts, while all but two of the Republican retirements are in generally safe GOP territory.

Democrats currently have a 253-177 majority, with five vacancies that will be filled by special elections before November. It takes 218 to win a majority.

There was no tangible evidence Stupak was in political jeopardy in his socially conservative district. His Democratic primary opponent supports abortion rights, and none of his three Republican challengers had reported any campaign cash on hand.

Democratic strategists said Stupak's name had not appeared on any internal list of party incumbents who might be in jeopardy in the fall.

"Stupak has always had very high personal popularity," said Bernie Porn, a pollster with Lansing-based EPIC-MRA. "I would have difficulty believing the tea party influence in and of itself would have driven him out."

Stupak defeated former state Rep. Tom Casperson with 65 percent of the vote in 2008 while fellow Democrat Obama got 50 percent of the congressional district's vote. Republican George W. Bush carried the district in 2004, while Stupak won re-election.

"People up here are very independent, and they vote that way," said state Rep. Gary McDowell, a Democrat from Rudyard in Michigan's Upper Peninsula. "There's probably more ticketsplitters and more independent-thinking people in this district I would say than probably any other part of the state."