Senate Republican hopes to overhaul the U.S. health insurance system appear to hinge on the passage of a “skinny” bill that would only repeal a select few provisions in the 2010 health care law.

GOP senators and aides anticipate that several of the other Republican health care proposals expected to be considered by the chamber in the coming days will fail, clearing the way for a package that would likely just repeal the employer and individual mandates and an excise tax on medical device manufacturers.

But even that plan to advance a slimmed-down repeal bill faces difficult odds.

The chamber on Tuesday narrowly approved a motion to proceed to the House-passed bill to repeal and replace the 2010 law, with Vice President Mike Pence breaking a 50-50 tie.

Republican leadership can now bring up for a vote several different proposals intended to, in some way or another, revamp the country’s health care system.