Two Republican Senators, Shelley Moore Capito and Susan Collins, said they oppose Mitch McConnell's new plan to repeal Obamacare first and then replace at a later date. Capito voted for a full repeal in 2015, whereas Collins voted against that move.

Why it matters: The Republicans can only afford these two no votes. If anyone else steps up in opposition, the plan is shot.

Jerry Moran, one of the senators who stood in the way of the earlier repeal-and-replace plan, won't stand in the way of the current repeal-then-replace plan.

Capito: "I did not come to Washington to hurt people…I have serious concerns about how we continue to provide affordable care to those who have benefited from West Virginia's decision to expand Medicaid, especially in light of the growing opioid crisis…I cannot vote to repeal Obamacare without a replacement plan…"

Collins: "I do not think that it's going to be constructive to repeal a law that at this point is so interwoven within our health care system without having a replacement plan in place. We can't just hope that we will pass a replacement within the next two years."

Senators to watch: Dean Heller, Lisa Murkowski, and Rob Portman.