Senate Majority Leader Mitch McConnell on Monday night abruptly called for a vote to repeal Obamacare without an immediate replacement after the latest Republican effort to overhaul the U.S. health-care system fizzled out.

"Regretfully, it's now apparent that the effort to repeal and immediately replace the failure of Obamacare will not be successful," McConnell said in a statement. "So, in the coming days, the Senate will vote to take up the House bill with the first amendment in order being what a majority of the Senate has already supported in 2015 and that was vetoed by then-President Obama: a repeal of Obamacare with a two-year delay to provide for a stable transition period to a patient-centered health care system that gives Americans access to quality, affordable care."

President Donald Trump , who had pressed for a repeal and replacement plan, urged Republican lawmakers to repeal Obamacare first, and then come up with a solution for replacing it. It is unclear if the GOP has the votes to repeal the law without an immediate replacement, as it risks destabilizing insurance markets.

Earlier Monday, two more Republican senators said they would oppose the current Republican health-care bill — enough to doom its passage barring changes.

In messages posted to Twitter, Sens. Jerry Moran , R-Kan., and Mike Lee , R-Utah, became the third and fourth GOP senators to say they would not support their party's Obamacare replacement plan as written. They said they would not even back a motion to allow a procedural vote that would have started debate on the bill. The GOP, which holds 52 seats in the Senate, had already seen two defections and could not afford a third.

It was the latest setback to the GOP's effort to repeal and replace Obamacare, a Republican campaign promise for most of the last decade that has stalled multiple times this year amid party divisions. The GOP chose to address the health-care overhaul before it took on tax reform, another key campaign plank, and every setback is seen as delaying the party's broader agenda.

Before Trump's tweet, a White House official said in a statement that "inaction is not an option. We look forward to Congress continuing to work toward a bill the President can sign to end the Obamacare nightmare and restore quality care at affordable prices."