Thomson Reuters
U.S. Senator Susan Collins has been critical of the Senate's healthcare bills.
The Senate is expected to vote on a motion to proceed that would bring up the healthcare bill that passed in the House. At that point, one of a number of proposed draft healthcare bills stands to be shaped into the legislation that will get voted on.
Even so, many Republican senators have not embraced the bill with open arms.
Some more conservative senators want to vote on a bill to fully repeal the Affordable Care Act, or Obamacare. Some moderates, on the other hand, think the bill to repeal and replace, the Better Care Reconciliation Act (BCRA), goes too far and want to keep some of the more popular parts of the ACA intact.
Here are the GOP senators who have shaped the fight over the Senate healthcare bill - and what they might still want to change.