WASHINGTON — Two more Republican senators declared on Monday night that they would oppose the Senate Republican bill to repeal the Affordable Care Act, killing, for now, a seven-year-old promise to overturn President Barack Obama’s signature domestic achievement.

The announcement by the senators, Mike Lee of Utah and Jerry Moran of Kansas, left their leaders at least two votes short of the number needed to begin debate on their bill to dismantle the health law. Two other Republican senators, Rand Paul of Kentucky and Susan Collins of Maine, had already said they would not support a procedural step to begin debate.

With four solid votes against the bill, Republican leaders now have two options.

They can try to rewrite it in a way that can secure 50 Republican votes, a seeming impossibility at this point, given the complaints by the defecting senators. Or they can work with Democrats on a narrower measure to fix the flaws in the Affordable Care Act that both parties acknowledge.

Senator Mitch McConnell, the Republican leader, conceded Monday night that “the effort to repeal and immediately replace the failure of Obamacare will not be successful.” He outlined plans to vote now on a measure to repeal the Affordable Care Act, with it taking effect later. That has almost no chance to pass, however, since it could leave millions without insurance and leave insurance markets in turmoil.

But President Trump was not ready to give up. He immediately took to Twitter to say: “Republicans should just REPEAL failing ObamaCare now & work on a new Healthcare Plan that will start from a clean slate. Dems will join in!”

In announcing his opposition to the bill, Mr. Moran said it “fails to repeal the Affordable Care Act or address health care’s rising costs.”

“There are serious problems with Obamacare, and my goal remains what it has been for a long time: to repeal and replace it,” he said in a statement.

In his own statement, Mr. Lee said of the bill, “In addition to not repealing all of the Obamacare taxes, it doesn’t go far enough in lowering premiums for middle-class families; nor does it create enough free space from the most costly Obamacare regulations.”

By defecting together, Mr. Moran and Mr. Lee ensured that no one senator would be the definitive “no” vote.

House Republicans, after their own fits and starts, passed a bill to repeal the Affordable Care Act in May, a difficult vote that was supposed to set the stage for Senate action. But with conservative and moderate Republicans so far apart in the Senate, the…