WASHINGTON, United States (AFP) — President Donald Trump warned Republicans on Monday that they have one “last chance” to pass the party’s health care reforms, as US lawmakers brace for a vote whose fate remained uncertain.

With the effort to repeal and replace Obamacare floundering in Congress, the Senate was expected to vote Tuesday to begin debate on the latest Republican plan, a bid to dismantle the 2010 reforms of Trump’s predecessor but delay the actual implementation to allow time for a viable replacement to be crafted.

By any measure it is an iffy proposition, with previous versions having collapsed in recent weeks.

Senate Republican leaders acknowledge they do not know whether there is sufficient support within the party to open debate on the new plan, a sign of Republican division about the impact such reforms might have on millions of American families.

With less than three weeks before the Senate is to leave Washington for its already-delayed summer recess, Trump called on his party to get in line.

“Republicans have a last chance to do the right thing on Repeal & Replace after years of talking & campaigning on it,” Trump said on Twitter early Monday.

That followed an ominous — if ambiguous — threat Sunday night about what might occur should Congress come up short.

“If Republicans don’t Repeal and Replace the disastrous ObamaCare, the repercussions will be far greater than any of them understand!” he tweeted.

It was not clear if Trump was referring to the prospect that failure to pass health care reform will lead to election challenges against GOP incumbents next year, or hurt American families.

Forecasts by the non-partisan Congressional Budget Office for various health reform bills predict that millions of Americans would lose health care if the measures become law. In the case of a bill that repeals Obamacare and provides no replacement, 32 million more people would be uninsured by 2026 as compared to current law, CBO forecast.

With his credibility on the line, Trump has repeatedly urged Republicans to help salvage one of his central campaign pledges.

Republicans hold 52 of the Senate’s 100 seats. With all Democrats opposed, Trump can afford just two defectors.

But as of last week, three Republican holdouts said they will vote no on the so-called motion to proceed, which opens debate on the legislation.

Trump was to lobby at least one of those senators, Shelley Moore Capito, when he flies Monday to Beaver, West Virginia to attend a Boy Scouts convention.

Several other Republicans have also expressed concerns, but have not said how they would vote.

“I think until the vote is actually on the floor of the Senate, some people may not tell you what they’re actually going to do,” Senate Republican John Barrasso told CBS talk show “Face the Nation” on Sunday.

Once the repeal-only bill is on the floor, it could be amended “in various ways,” Barrasso said, including changing it to a repeal-and-replace bill.