WASHINGTON — President Donald Trump agreed to add fresh Medicaid curbs to the House Republican health care bill Friday, bolstering the measure with support from some conservative lawmakers but leaving its prospects wobbly.

House leaders discussed other amendments calibrated to round up votes and scheduled a showdown vote for Thursday.

“I just want to let the world know I am 100 percent in favor” of the measure and the changes, Trump said at the White House after meeting around a dozen House lawmakers and shaking hands on revisions. “We’re going to have a health care plan that’s going to be second to none.”

While the rapid-fire events seemed to build momentum for the pivotal GOP legislation, its fate remained clouded. One leading House conservative said the alterations were insufficient and claimed enough allies to sink the measure even as support among GOP moderates remained uncertain.

“My whip count indicates that there are 40 no’s,” enough to defeat the bill, said Rep. Mark Meadows, R-N.C., who leads the hard-line House Freedom Caucus.

He said the change “doesn’t move the ball more than a couple yards on a very long playing field.”

Across the Capitol, Sen. Dean Heller, R-Nev., who faces re-election next year, became the fourth Republican senator to announce his opposition. That left Senate GOP leaders at least two votes shy of what they’d need to prevail.

Congressional Democrats remain solidly opposed to the GOP effort.

The Republican bill would kill much of former President Barack Obama’s health care law, including tax penalties for people who don’t buy insurance and its expansion of Medicaid, the federal-state health program for the poor.

It would create new tax credits that would be less generous than current federal subsidies for many consumers, and repeal levies on the wealthy and medical firms that helped finance Obama’s expansion of coverage to 20 million Americans.

The deal between Trump and lawmakers would let states choose to impose work requirements on some of Medicaid’s roughly 60 million recipients.

Details were initially unclear, but Republicans have recently discussed using them for healthy people with no dependents.

The agreement would also allow states to decide to accept a lump-sum federal payment for Medicaid, instead of an amount that would grow with the number of beneficiaries. The program currently costs the federal government around $370 billion annually and automatically covers costs, no matter the amounts.

“These changes definitely strengthen our numbers,” said the House GOP’s top vote counter, Rep. Steve Scalise of Louisiana, who was among those who met Friday with Trump.

“But they also show that President Trump is all-in now,” a help in winning converts.