Washington - US President Donald Trump warned Republicans that he is done negotiating and wants a vote on Friday on replacing Obamacare, warning that if the effort fails, his predecessor's health care reforms will stand, lawmakers in an emergency meeting said.In a high-stakes closed-door huddle with Republican lawmakers late on Thursday, White House Budget Director Mick Mulvaney essentially issued an ultimatum from Trump after House Republican leaders postponed the vote amid the realisation it would not pass without key changes."The president has said he wants a vote tomorrow, up or down," House Republican Chris Collins told reporters, paraphrasing Mulvaney's remarks."If it doesn't pass, we're moving beyond health care," he added by paraphrase, in a threat to lawmakers in Trump's own Republican Party."We would be moving on to other parts of his agenda."Desperate for a 'yes'The idea that Trump - who campaigned relentlessly last year on a pledge to bury Barack Obama's signature legislative accomplishment - would wash his hands of the fight and let Obamacare stand is a startling departure from the party playbook.Defeat would mark a stunning political setback for Trump, who prides himself on his dealmaking skills.Mulvaney's blunt take-it-or-leave-it approach could be part of Trump's hardball strategy to get Republican rebels to fall in line.House Speaker Paul Ryan, a champion of the legislation dubbed the American Health Care Act, put on a brave face despite the bill's hanging by a thread."We have been promising the American people we will repeal and replace this broken law because it's collapsing and failing families, and tomorrow we're proceeding," he told reporters after the conference meeting.The president and his lieutenants had repeatedly voiced optimism about the bill's prospects, saying they had made progress convincing doubters to join his camp in dismantling the Affordable Care Act.But the votes for Trump's plan weren't there."I am still a no at this time. I am desperately trying to get to yes," said Mark Meadows, chairperson of the conservative House Freedom Caucus, whose members have demanded changes to the plan before giving their blessing.Although Meadows sought to portray optimism about the process, he revealed the width of the gap between Trump and the plan's opponents."At this point, we are trying to get another 30 to 40 votes that are currently in the 'no' category to 'yes,'" Meadows said after meeting with his caucus.That did not happen, and Ryan pulled the bill off the floor.Midnight oilWith White House negotiations unable to provide the necessary breakthrough, nighttime debate between party factions is likely to be intense as they seek an elusive compromise."The caucus is going to get together and talk," Meadows said, adding that his Freedom Caucus would meet with members of the more moderate Tuesday Group to discuss ways forward.Republicans have spent years railing against the Affordable Care Act, branding it a result of a Democratic push for socialised medicine.With Democrats opposed to Trump's plan and his own party's right flank in revolt over legislation they say does not go far enough, the White House and Republican leaders looked to make the bill palatable to enough conservatives without angering moderates.Confidence by the White House appeared to highlight the disconnect between Trump's team and rank-and-file conservatives.Asked on Thursday whether House Speaker Paul Ryan might delay the vote, White House spokesperson Sean Spicer said "nothing leads me to believe that that's the case."The vote was postponed a few hours later.Many conservatives say their party's plan is still too costly for the government. They have said they want to repeal "essential health benefits" that all insurance policies must pay for under Obamacare - including maternity care, emergency room visits and preventive care such as screenings and vaccines - arguing they have driven up costs.Republican leaders conceded to that demand, Collins said. An amendment to the bill will be introduced that repeals those benefit requirements.Limiting defections The House Freedom Caucus, some 30 lawmakers who are heirs-apparent to the ultra-conservative Tea Party movement, have dubbed the new bill "Obamacare Lite," saying it will only reduce, not eliminate, health coverage subsidies by replacing them with refundable tax credits.At the other end of the spectrum, some Republican moderates are worried their constituents would no longer be able to afford health insurance under the new plan.A nonpartisan congressional budget estimate says it would force 14 million Americans to lose their coverage from next year.An update of that estimate on Thursday, taking recent tinkering with the bill into account, said the plan would cost more money than the previous version.The Democratic minority is prepared to vote against the bill as a bloc, so Republican leaders need to limit defections to fewer than 22 of their party's 237 representatives among the House's 430 current members.Trump himself weighed in on Twitter during the Republican meeting, calling Obamacare "disastrous" and warning that costs will only rise and options shrink."We must #RepealANDReplace. #PassTheBill," he added.