WASHINGTON — President Barack Obama’s much-challenged health care overhaul gained traction Wednesday as a liberal lawmaker became the first to switch his opposition and Catholic nuns declared their support in an unusual public break with the bishops.

Rep. Dennis Kucinich, D-Ohio, long a supporter of Medicare-for-all, voted against the House Democratic bill in November because it did not go far enough in creating a robust government-run plan to compete with private insurance. But Kucinich said Wednesday that the bill coming before the House represents the best chance to expand coverage to the uninsured, even if it does not include a public plan.

At a Capitol Hill news conference, Kucinich said his decision was a combination of pragmatism and concern about the impact that defeat of the health care bill would have on Obama’s presidency.

“You do have to be very careful that the potential of President Obama’s presidency not be destroyed by this debate,” said Kucinich. “Even though I have many differences with him on policy, there’s something much bigger at stake here for America.”

Kucinich said he’d met with Obama four times to discuss the health overhaul, most recently on Monday when he flew back to Ohio with the president aboard Air Force One. Obama called Kucinich’s decision “a good sign.”

At stake is a bill that would cover some 30 million uninsured people, end insurance practices such as denying coverage to those with a pre-existing conditions, require almost all Americans to get coverage by law and try to slow the cost of medical care nationwide. The comprehensive legislation could affect nearly every American, from those undergoing annual checkups to people facing major surgery.

Democratic leaders hope to vote this weekend.

Meanwhile, in a rare public disagreement that will reverberate among the nation’s 70 million Catholics, leaders of religious orders representing 59,000 nuns sent lawmakers a letter urging lawmakers to pass the Senate health care bill. Expected to come before the House by this weekend, the measure contains abortion funding restrictions that the bishops say don’t go far enough.

“Despite false claims to the contrary, the Senate bill will not provide taxpayer funding for elective abortions,” said the letter signed by 60 leaders of women’s religious orders. “It will uphold longstanding conscience protections and it will make historic new investments ... in support of pregnant women. This is the real pro-life stance, and we as Catholics are all for it.”

The U.S. Conference of Catholic Bishops and the National Right to Life Committee have denounced the bill as a backdoor subsidy for abortion. But the nuns and the Catholic Health Association — representing some 600 hospitals — say restrictions in the Senate bill would still prevent taxpayer funding for abortion, although the legal mechanism for doing so is different from what the bishops prefer.

“This is politics; this isn’t a question of faith and morals,” said Sister Simone Campbell, executive director of Network, a national Catholic social activism lobby. “We are the ones who work every day with people who are suffering because they don’t have health care. We cannot turn our backs on them, so for us, health care reform is a faith-based response to human need.”

Another sign of a rift among abortion opponents emerged as Rep. Dale Kildee, D-Ohio, announced his support for the bill. Kildee was among the anti-abortion Democrats who backed Rep. Bart Stupak, D-Mich., in forcing tough restrictions on the original House-passed bill.

Kildee said in a statement Wednesday that after careful study, he’s concluded the Senate bill would also bar federal funding for abortion — while saving lives by providing coverage to those now uninsured. “Voting for this bill in no way diminishes my pro-life voting record or undermines my beliefs,” he said. “I am a staunch pro-life member of Congress, both for the born and the unborn.”

A new report from the nonpartisan Robert Wood Johnson Foundation shows the nation’s middle class, who typically don’t qualify for government health insurance, became uninsured at a pace faster than the poor from 2000 to 2008. The report says 13 million middle-income earners were uninsured in 2008 — about 2 million more than in 2000.

Wednesday’s developments heartened House Democratic leaders, who are still short of the 216 votes they need to pass the bill. The No. 2 Democrat in the House, Rep. Steny Hoyer of Maryland, dodged a question about whether his party has the votes. “I don’t have a precise number,” Hoyer said on ABC’s “Good Morning America.” “We think we will have the votes when the roll is called.”

White House aides said Obama and senior advisers are making clear to lawmakers that they will not be left standing alone in a difficult election year if they cast a tough vote for health care overhaul. The aides spoke on condition of anonymity to discuss the private meetings.