WASHINGTON -  President Donald Trump put his reputation as a dealmaker on the line Friday in a high-risk vote on an embattled Republican health care plan, with rebels in his own party threatening to torpedo the reform.

Trump turned up the heat on die-hard conservatives with the White House casting the vote in the House of Representatives as a do-or-die chance to repeal and replace Barack Obama’s signature heath care law.

Passage would hand Trump a monumental victory after a bruising battle with recalcitrant Republicans, mainly conservatives who say the new plan is too similar to Obamacare and would cost the government too much.

Defeat could send the seven-year Republican effort to pull Obama’s Affordable Care Act out by its roots and replace it with something better careening into a tailspin - and deal the president a major setback.

“After seven horrible years of Obamacare (skyrocketing premiums & deductibles, bad healthcare), this is finally your chance for a great plan!” Trump tweeted in an 11th-hour message to Republicans in Congress.

The House took a first procedural step Friday, voting 230 to 194 to advance the bill - which has undergone changes to appease conservatives and moderates alike.

A final floor vote is set for between 3:45 and 4:45 pm (1945 and 2045 GMT).

House Speaker Paul Ryan, the reform’s chief champion in the House, had planned a Thursday vote but in a stunning development was forced to pull the bill off the floor when it became clear he would not get it across the finish line.

After several days of intense meetings at the White House with Republican conservatives and moderates aimed at tweaking the bill to find enough common ground for it to pass, Trump ran out of patience.

On Thursday evening the president issued an ultimatum to his party: he wants a House vote Friday, and if he loses, Obamacare - which he has called disastrous and Republicans have derided since it was enacted exactly seven years ago - will remain in force and he will move on to other things on his agenda.

Still, the White House expressed confidence they could rally undecided or skeptical Republicans to their side.

“I think it is” going to pass, Health and Human Services Secretary Tom Price, himself until recently a House Republican, told CNN.

“The president has done everything he can do, any individual could do, to make sure people appreciate the consequence of this vote.”

But Trump’s effort took a further blow Friday when the powerful chairman of the House Appropriations Committee, Rodney Frelinghuysen, came out against the bill.

“Unfortunately, the legislation before the House today is currently unacceptable as it would place significant new costs and barriers to care on my constituents in New Jersey,” he said in a statement.

The House Freedom Caucus - some 30 lawmakers who are heirs-apparent to the ultra-conservative Tea Party movement - have spearheaded opposition to a bill they dub “Obamacare Lite,” complaining it will only reduce, not eliminate, health coverage subsidies by replacing them with refundable tax credits.

Conservatives, eager to rein in rising premiums, want to repeal “essential health benefits” that all insurance policies must pay for under Obamacare - including maternity care and emergency room visits.

Republican leaders conceded to that demand and repealed those benefit requirements.

“Today is about a rescue mission” for American families struggling under the current law, Republican Bradley Byrne, one of those defending the bill, said on the House floor.

“Obamacare is on a collision course with disaster.”

But as debate began Friday, Democrats seized their chance to loudly rail against the bill.

House Democrat Robin Kelly warned that Republican lawmakers will “own its aftermath,” as she cited a recent congressional analysis that projected 24 million more Americans will be left without health insurance over the next decade if the plan becomes law.

The Democratic minority will likely 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.

Should the bill squeak by, it faces an equally tough road in the US Senate, where Republicans hold a slim 52-48 majority.