McConnell could only afford two defections from the 52-member Senate Republican conference. Republicans planned to push their bill through using a process known as reconciliation—which has a lower, 50-vote threshold for passage—and with the help of Vice President Mike Pence in the event of a tie.

The setback cast fresh uncertainty on the Republican effort to dismantle former President Barack Obama’s signature health-care law. Promises of repeal constituted the central pillar of the GOP platform when the party was out of power in the White House. But despite having control of both the presidency and Congress now, Republicans have not yet managed to deliver on their health-care agenda. That has left President Trump without any major legislative achievements to capitalize on, and has created division within the ranks of congressional Republicans.

The president weighed in on the fate of the law Monday night on Twitter: “Republicans should just REPEAL failing ObamaCare now & work on a new Healthcare Plan that will start from a clean slate. Dems will join in!”

Prospects appear dim, however, that GOP leaders can find enough votes to pass a repeal plan without an immediate replacement, given how many Republican senators would likely balk at the potential for uncertainty. The New York Times reported Monday evening that a repeal-only vote “has almost no chance to pass, however, since it could leave millions without insurance and leave insurance markets in turmoil.”

A central sticking point in congressional health-care deliberations has been a clash between moderate Republicans—who feared the Senate’s most recent legislation would have gone too far in altering key parts of Obamacare, like its Medicaid expansion—and conservative Republicans, who expressed dismay that the bill did not go far enough in undoing it. Analyses of a recent iteration of the Senate’s bill determined that, if enacted, the legislation would leave upwards of 20 million Americans without health insurance in the next decade.

“We must now start fresh with an open legislative process,” Moran said in his statement Monday, a criticism directed at Senate Republican leadership over the secrecy with which the latest legislation was crafted. “This closed-door process has yielded the [the Better Care Reconciliation Act], which fails to repeal the Affordable Care Act or address health care’s rising costs. For the same reasons I could not support the previous bill, I cannot support this one.”

In his statement, Lee stated that he had “decided I cannot support the current version of the Better Care Reconciliation Act.” Lee argued that “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.”