Vox has a very helpful flowchart explaining the many steps to get to Repeal and/or Replace. Click here. Basically, McConnell needs only 50 Senators to vote for his bill because VP Pence will cast the necessary vote to get them to 51. During the vote-a-rama, amendments can be added to the bill, but McConnell still has the authority to disregard all amendments in the final moments. The best outcome is to defeat the motion to proceed at the outset.