On Thursday, House Republicans are slated to vote on the American Health Care Act, the Republican plan to replace Obamacare. House Speaker Paul Ryan can afford to lose 22 Republican votes if he wants it to pass (one Democrat will be absent).

Given that House Republicans have long been united by their disdain for Obamacare, that might seem easy. But it won’t be. When the bill was first introduced on March 6, it drew criticism from a wide range of groups — health industry lobbies, conservatives, and moderate Republicans all came out against the legislation. The Congressional Budget Office estimated that 24 million people would lose coverage if the bill were enacted. Still, Ryan was able to swiftly usher his plan through three committees, sometimes in the dead of night.

Over the weekend, he promised in response to the ongoing criticism to come up with a new version of the legislation in time for the Thursday evening vote. It’s not yet clear what, exactly, his next version of the American Health Care Act will change. But these House Republicans are the audience he’ll have to win over:

Even if Republicans are able to pass the bill in the House, it faces many challenges moving forward. The margin of support needed for the bill pass is much tighter in the Senate, and 12 GOP senators have already expressed criticism. Moreover, because Republicans are trying to pass their plan through the budget reconciliation process, which would allow them to avoid a Democratic filibuster, they are limited in what they can and can’t include in the legislation. Should the bill make it to the Senate, Democrats will almost certainly argue that the plan violates these rules.