WASHINGTON (Reuters) - Jason Chaffetz, a rising star among congressional Republicans, on Sunday declared a bid to become speaker of the U.S. House of Representatives, complicating further an internal party struggle to replace John Boehner when he steps down.

The chairman of the House Committee on Oversight and Government Reform committee, Congressman Jason Chaffetz (R-UT), questions Planned Parenthood Federation president Cecile Richards (not pictured) on Capitol Hill in Washington September 29, 2015. REUTERS/Gary Cameron

In a challenge to Boehner’s closest lieutenant and presumed successor Kevin McCarthy, Chaffetz said many Republican lawmakers want a more thorough change in House leadership.

“I’ve had enough members who have come and said, ‘Please, Jason, do this. We don’t want to fight internally, but realistically we can’t vote to promote the existing leadership,’” Chaffetz said on television’s Fox News Sunday.

Though he would be a long-shot, Chaffetz could mount a credible threat to McCarthy, more so than the other declared contender for the speaker’s post, Florida Representative Daniel Webster.

The contest could be prolonged, and some congressional aides speculated that Boehner might be asked to stay on later than Oct. 30, when he plans to leave.

Stunning much of Washington, Boehner on Sept. 25 said he would resign after years of squabbles with conservative hardliners. That step prevented a U.S. government shutdown by allowing him to work with Democrats to keep agencies funded through Dec. 11 and put off a showdown over taxpayer support for women’s healthcare group Planned Parenthood.

Some analysts had said Boehner, in his final weeks, might go further to prevent potential shocks to the economy and markets by trying to raise the government’s debt ceiling.

Such moves may be less likely with Republicans consumed by infighting over leadership roles.

The speaker election is set for Thursday. Boehner is considering postponing elections for other leadership positions that could open up, Politico said on Sunday.

McCarthy, currently the House majority leader, remains the favorite for speaker, but many conservatives have reservations and doubt the affable 50-year-old Californian has the votes to win.

He drew fire from colleagues last week when he implied a Republican-led probe of 2012’s Benghazi attack was aimed at hurting Democrat Hillary Clinton’s presidential candidacy. He said his words were misinterpreted.

Chaffetz, 48, of Utah, rose quickly to committee leadership after being elected in 2008. He has gained attention for aggressively targeting Planned Parenthood, a perennial target for Republican ire because a small part of its operations is providing abortions.

But some Planned Parenthood critics said his recent five-hour hearing with the group’s president was too focused on politics and not enough on oversight of the health nonprofit.