President Donald Trump on Monday evening urged Republican lawmakers to repeal Obamacare first, and then come up with a solution for replacing it.

It followed two more Republican senators saying Monday they will oppose the current Republican health-care bill — enough to doom its passage, for now. The GOP likely would not have the votes to repeal the law without a replacement, as it risks destabilizing insurance markets.

In messages posted to Twitter, Sens. Jerry Moran, R-Ks., 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 proceed — a procedural vote that would start debate on the bill.

The GOP, which holds 52 seats in the Senate, had already seen two defections and could not afford a third.

Their opposition marks just 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.

It is not clear how Republicans will proceed. They can still attempt to win over senators opposing the plan with changes to the bill, though it is unclear what tweaks will appease both moderate and conservative senators.

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.”

After the Senate’s initial struggles to reach a health-care consensus in June, Trump and Sen. Rand Paul, R-Ky., both publicly floated the prospect of repealing Obamacare without a replacement plan. Trump has usually said that he prefers that a replacement come at the same time as a repeal.

The GOP-controlled Congress passed a bill in 2015 to repeal Obamacare without a replacement, though they cast their votes knowing that the bill would face a presidential veto from then-President Barack Obama.