WASHINGTON — President Trump agreed to add 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 Thursday.

“I just want to let the world know I am 100 percent in favor” of the measure, Trump said at the White House after meeting around a dozen House lawmakers and shaking hands on revisions.

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, and support among 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., facing 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.

Thursday will mark the seventh anniversary of when Obama signed his health overhaul into law, one of his milestone domestic achievements enacted over unanimous GOP opposition. Beyond that symbolism, Republican leaders hope to allow time for Congress to complete the measure before an early April recess exposes lawmakers to two weeks of lobbying and town hall pressure tactics by activists, doctors, hospitals and other opponents.

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.