The House of Representatives is set to vote today on a Republican bill to repeal and replace the Affordable Care Act—a plan the Congressional Budget Office says would add 24 million people to the ranks of the uninsured. President Donald Trump and Vice President Mike Pence spent Wednesday on Capitol Hill negotiating with Republicans wary of the legislation. North Carolina Rep. Mark Meadows said more than 20 members of his right-wing House Freedom Caucus were prepared to defeat the bill because it does not go far enough to dismantle the Affordable Care Act. At the White House, Press Secretary Sean Spicer rejected calls by some Republicans to postpone tonight’s vote.

Press Secretary Sean Spicer: “This bill represents the best chance of repealing and replacing Obamacare and instilling a patient-centric healthcare system that increases choice and lowers costs, and that this is the only train leaving the station.”

Today’s vote comes as Americans for Prosperity and Freedom Partners—two groups backed by billionaires Charles and David Koch—said they’ve created a multimillion-dollar campaign fund for Republicans who reject the healthcare legislation in favor of a more stringent repeal of Obamacare. Republican opposition to the bill appeared to soften late Wednesday, after President Trump reportedly promised that the final legislation would strip a requirement that insurance companies cover “essential health benefits” like emergency room visits, mental health and maternity and newborn care.