GOP leaders are trying to kill and replace several major parts of Obamacare through the process known as budget reconciliation.
If the Senate parliamentarian agrees that the bill qualifies for that process because it is budget-specific, Republicans would need just 50 votes in the Senate, where they hold 52 seats, to pass the proposal.
But four GOP senators have already expressed opposition to the idea of rolling back gains made in Medicaid coverage under Obamacare, as the new GOP bill could well do. Other Republicans have objected to the bill's use of refundable tax credits to subsidize the purchase of private individual health insurance plans, while other GOP members opposed the defunding of Planned Parenthood in the bill.
If the parliamentarian does not agree that bill can be passed through reconciliation, Republicans would need 60 senators to vote for the bill. That would likely be an impossible hurdle, given how firmly Democrats are opposed to it.