WASHINGTON >> The top Republican legislative priority in peril, President Donald Trump dangled possible changes to the health care bill today aimed at placating conservatives threatening to torpedo the legislation. The White House seemed to make progress after GOP opposition had snowballed a day before a showdown House vote.

Trump huddled at the White House with 18 lawmakers, a mix of supporters and opponents, Vice President Mike Pence saw around two dozen and House GOP leaders held countless talks with lawmakers at the Capitol. The sessions came as leaders rummaged for votes on a roll call they can ill-afford to lose without diminishing their clout for the rest of the GOP agenda.

Most GOP opponents were conservatives asserting that the legislation demolishing former President Barack Obama’s health care law did not go far enough. They were demanding repeal of the law’s requirements that insurers pay for specified services like maternity care, prescription drugs and substances abuse treatment.

Late today, House Speaker Paul Ryan, R-Wis., met with moderate Republicans from Pennsylvania, Illinois, Maine and New York as well as members of leadership. Any changes on essential health benefits would likely trigger an immediate backlash from patient advocacy groups and doctors.

In early meetings with Trump and Pence and later discussions with the White House, talks focused on language addressing conservatives’ concerns that those coverage requirements drive up premiums. Details were unclear, but members of the House Freedom Caucus, the hard-line group spearheading the opposition, were expected at the White House early Thursday.

“Tonight is an encouraging night,” said Rep. Mark Meadows, R-N.C., leader of the caucus, who for days has said he has the votes to kill the measure. “But I don’t want to be so optimistic as to say the deal is done.”

It was initially uncertain if the provision could survive in the Senate or how moderate Republicans would react. Democrats said the language would die in the Senate because that chamber’s rules don’t allow provisions not directly related to the federal budget.

The Republican legislation would halt Obama’s tax penalties against people who don’t buy coverage and cut the federal-state Medicaid program for low earners, which the statute expanded. It would provide tax credits to help people pay medical bills, though generally skimpier than the aid Obama’s statute provides. It also would allow insurers to charge older Americans more and repeal tax boosts the law imposed on high-income people and health industry companies.

In a count by The Associated Press, at least 25 Republicans said they opposed the bill and others were leaning that way, enough to narrowly defeat the measure. The number was in constant flux amid eleventh-hour lobbying by the White House and GOP leaders.

Including vacancies and expected absentees, the bill would be defeated if 23 Republicans join all Democrats in voting “no.”

In a show of support for the opponents, the conservative Koch network promised today to spend millions of dollars to defeat the health care overhaul, the influential network’s most aggressive move against the bill.

Moderates were daunted by projections of 24 million Americans losing coverage in a decade and higher out-of-pocket costs for many low-income and older people, as predicted by the nonpartisan Congressional Budget Office.

For now, leaders showed no sign of delaying a House vote, their initial attempt to deliver on a pledge to erase Obama’s law they’ve repeated since its 2010 enactment.

Underscoring the delicate pathway to victory, participants in the Pence meeting said there were no visible signs of weakened opposition and described one tense moment. Rep. Randy Weber, R-Texas, said White House chief strategist Steve Bannon told them: “We’ve got to do this. I know you don’t like it, but you have to vote for this.”

Weber said Rep. Joe Barton, R-Texas, bristled.

“When somebody tells me I have to do something, odds are really good that I will do exactly the opposite,” Barton said, according to Weber.

Rep. Steve King, R-Iowa, said that talk of deleting the insurance coverage requirements had converted him into a supporter. But before the late talks, others were skeptical.

“We’re being asked to sign a blank check,” said Rep. Scott Perry, R-Pa., who’s been an opponent. “In the past, that hasn’t worked out so well.”

Some Republicans were showing irritation at their party’s holdouts, all but accusing them of damaging the GOP.

“At some point we have to cowboy up and prove we can govern,” said Rep. Kevin Cramer, R-N.D. “Otherwise we’re just going to be the ‘no’ party and some people are OK with that, it appears.”

The Rules Committee, usually tightly controlled by GOP leadership, was expected to let the chamber vote on revisions that top Republicans concocted to win votes. These include adding federal aid for older people and protecting upstate New York counties — but not Democratic-run New York City — from repaying the state billions of dollars for Medicaid costs.

There were other glimmers of hope for GOP leaders.

Rep. Lou Barletta, R-Pa., said he had switched from “no” to “yes” after Trump endorsed his bill to use Social Security numbers to hinder people from fraudulently collecting tax credits. Barletta, an outspoken foe of illegal immigration, said he had been promised a vote next month on the measure by House Speaker Paul Ryan, R-Wis.