WASHINGTON, March 23 (Reuters) - U.S. President Donald Trump may face his first major legislative hurdle on Thursday: a do-or-die vote in the House of Representatives on a plan that would roll back the signature healthcare law of former President Barack Obama.
Trump has been billed by some lawmakers as "the closer" to seal the deal on the replacement healthcare plan in a vote Republican leaders hoped to hold on Thursday, but there were signs late on Wednesday night that the deadline could be pushed back.
It was unclear whether Trump had convinced enough Republicans to back the bill. That uncertainty has rattled financial markets.
Failure to pass the legislation, called the American Health Care Act, would cast doubt on Trump's ability to deliver other parts of his agenda that need the cooperation of the Republican-controlled Congress, including ambitious plans to overhaul the tax code and invest in infrastructure.
Stocks on Tuesday posted their biggest one-day drop since the Nov. 8 presidential election on concerns about the healthcare drama.
The vote on the House floor had been initially expected by around 7 pm (2300 GMT) on Thursday. But by midnight on Wednesday, lawmakers had not yet settled on the timing of the vote as conservative and moderate Republicans split on whether there should be additional changes to the proposal.
House Rules Committee Chairman Pete Sessions said the vote could happen as early as Thursday or as late as Monday.
Democratic representatives are united against the bill, which seeks to repeal and replace Obama's 2010 Affordable Care Act.
Trump and House Speaker Paul Ryan need strong support from their side of the aisle on the bill, and can only afford to lose 21 Republican votes.
But conservative Republicans have complained about the replacement for being too similar to Obamacare, and some moderate Republicans are concerned it will hurt the health care coverage of millions of voters.
An aide to the conservative House Freedom Caucus said at one point on Wednesday that more than 25 of its members were opposed to the plan. The chairman of the group, Representative Mark Meadows, said negotiations late on Wednesday were making headway.
Moderate Republicans huddled late into the evening in House Speaker Paul Ryan's office. Afterwards, Representative Charlie Dent issued a statement saying he could not back the bill.
Trump and fellow Republicans campaigned during last year's elections on a promise to repeal and replace Obamacare, a program that aimed to boost the number of Americans with health insurance through mandates on individuals and employers, and income-based subsidies.
Republicans said Obamacare marked an excessive government intrusion into the healthcare marketplace and blamed it for pushing insurance premium costs higher.
Their replacement plan would rescind the taxes created by Obamacare, repeal a penalty against people who do not buy coverage, slash funding for the Medicaid program for the poor and disabled, and modify tax subsidies that help individuals buy plans.
The nonpartisan Congressional Budget Office estimated 14 million people would lose medical coverage under the Republican plan by next year. It also said that 24 million fewer people would be insured by 2026.
Even if the legislation passes the House, its faces a second hurdle in the Senate, where a number of Republicans have spoken out against the House version.
Trump and Republican leaders have said they hope to have the bill finalized in early April so Trump can sign it into law by the middle of the month.
Additional reporting by Susan Cornwell and Jeff Mason; Editing by Bill Rigby and Michael Perry