Senate Majority Leader Mitch McConnell unveiled a draft of the GOP's proposed health care bill Thursday morning.
But by Thursday afternoon, at least four senators from his own party said they can't support the bill as is.
Sens. Rand Paul, Mike Lee, Ted Cruz and Ron Johnson said the current draft doesn't seem to "accomplish the most important promise that we made to Americans: to repeal Obamacare and lower their health care costs."
While they say they are "open to negotiation," the four could be a problem for McConnell and other Senate Republican leadership if they don't vote along party lines.
Republicans hold only 52 seats in the Senate. They can afford to lose only two GOP votes to pass the bill with 51 votes — and that banks on a tie-breaking vote from Vice President Mike Pence.
Several other Republican senators could end up opposing the bill for completely different reasons.
Senators from states where some provisions of the Affordable Care Act are popular — like the expansion of Medicaid — will likely have a hard time supporting a bill that makes cuts to those provisions.
Sen. Dean Heller of Nevada is up for reelection next year. He said Thursday: "I have made clear that I want to make sure the rug is not pulled out from under Nevada or the more than 200,000 Nevadans who received insurance for the first time under Medicaid expansion. At first glance, I have serious concerns about the bill’s impact on the Nevadans who depend on Medicaid."
Other Republicans senators who could end up opposing the bill for the same reason are Sens. Shelley Moore Capito of West Virginia, Lisa Murkowski of Alaska, Susan Collins of Maine and Rob Portman of Ohio.
The Congressional Budget Office hasn't yet released its analysis of the bill, which could also impact votes.
In a separate statement released Wednesday, Cruz said he is "hopeful that as we openly debate this legislation, real improvements will be made prior to floor consideration."
Sens. Cruz and Lee were supposed to help write the bill. In a Facebook Live video earlier this week, Lee said he shared the "frustration" of his constituents who felt there was a lack of transparency in the process.