Republicans have 52 seats in the Senate, meaning they can only afford to lose three members of their caucus before they cannot pass legislation without Democratic votes. (In the case of a 50-50 tie, the vice president casts the tie breaker -- presumably in favor of the GOP side.)
While only one Republican -- Kentucky Sen. Rand Paul -- has thus far signaled he might vote no on the Obamacare repeal mechanism currently moving through the Senate, potential flashpoints have already emerged that could jeopardize further votes.
House Speaker Paul Ryan's support of using the Obamacare repeal measure to strip federal funding for Planned Parenthood, an organization that provides abortions as part of its broader reproductive health care services to men and women, could cost the GOP two key votes.
That measure would likely pass in the House, but two pro-abortion rights GOP senators, Susan Collins of Maine and Lisa Murkowski of Alaska, won't commit to approving the bill with the Planned Parenthood provision in it.
"I'm going to wait and see what happens," Collins told reporters on Thursday, indicating she thinks it's too early to decide how she will vote on the bill. "Obviously, I'm not happy to hear the speaker wants to include defunding of Planned Parenthood, an extremely controversial issue in the package."
Murkowski has said this week she won't "speculate" about how she may vote on a hypothetical repeal package. When asked her position Thursday, Murkowski's spokeswoman Karina Petersen said the senator "is concerned about defunding Planned Parenthood as she is a longtime support of Planned Parenthood and has opposed broadly defunding the organization."
Paul has already voted against moving forward on the measure, which repeals Obamacare through a procedure called budget reconciliation. By voting on Obamacare through the budget process, the Senate can clear the measure with a simply majority -- meaning they theoretically need no Democratic votes to repeal the Affordable Care Act.
The libertarian-leaning Kentucky Republican has spoken out against the measure, however, because he says it would increase deficit spending and doesn't balance the budget. He's already trying to rally his colleagues and members of the budget hawkish House Freedom Caucus to join him, though he hasn't found any takers yet.
Instead, Paul wants to replace Obamacare on the same day Republicans repeal the law. He tweeted
Friday that night that he had spoken with Trump, who he said "fully supports" the proposal.
Repeal and wait on replace
The GOP may face a further internal debate over the "replace" piece of the puzzle.
While many Republicans support using budget reconciliation to repeal Obamacare, which is possible due to the tax and revenue-related elements of Obamacare, they cannot use the tactic to replace the bill.
Many Republicans have favored a plan to repeal the bill early in the Trump administration and then take time to come up with a plan to replace it.
On Thursday, Senate Majority Whip John Cornyn said that he would be against a "comprehensive" bill, and would support instead smaller measures to replace it.
But Paul has been joined by Sen. Tom Cotton, of Arkansas in supporting a repeal with an immediate replacement.
"I think when we repeal Obamacare we need to have the solution in place moving forward," the Arkansas Republican told MSNBC's Chuck Todd Thursday. "I don't think we can just repeal Obamacare and say we're going to get the answer two years from now. This is a very complicated problem."
Trump himself has also spoken in favor of immediate replacement -- though it's unclear if he was referring to when the replacement would take effect or when it should be passed. As insurance providers have already set their policies for the coming year, the repeal would not affect Americans this year regardless of when it was passed.
"No, we're going to do it simultaneously. It'll be just fine," Trump told CBS' "60 Minutes" in November when asked if there would be any gap in coverage. "We're not going to have, like, a two-day period and we're not going to have a two-year period where there's nothing. It will be repealed and replaced."