WASHINGTON - Tom MacArthur went out on a limb.

Thursday could determine if it snaps beneath him.

The Republican congressman from South Jersey took a steep risk last month, becoming the face of a plan to roll back one of the most popular patient protections in the Affordable Care Act. His amendment wooed House conservatives and revived a failed Republican plan to overhaul the law often called Obamacare.

The overall repeal plan is now scheduled for a decisive test Thursday morning, when House leaders have called a vote, capping weeks of maneuvering and putting one of President Trump's central promises on the line. Top GOP officials had said they would only schedule a vote if the plan had support to pass, so the announcement signaled confidence that it could advance.

Trump, just past the 100-day mark in his presidency, has been desperate to show progress on the issue. At a rally in Harrisburg on Saturday, he stressed how angry he would be if the bill didn't advance.

The plan gained momentum Wednesday when one initial opponent of MacArthur's idea, Rep. Fred Upton (R., Mich.), struck a deal to add $8 billion over five years to help cover people with pre-existing conditions.

Republicans argue that the plan, which appeared dead in March, would undo the health law's burdensome regulations, which they blame for driving up costs and say intrudes on private health decisions. It would follow through on seven years of GOP campaign promises.

But nonpartisan analysts estimated that it could also drive up the ranks of the uninsured by 24 million and, because of MacArthur's addition, erase a critical protection for people with pre-existing conditions, spiking their costs. Upton's addition seemed to win over some wary Republicans.

Aside from MacArthur, Republicans from the Philadelphia area have opposed the proposal. Several in Pennsylvania and New Jersey worry that the overall plan would roll back a Medicaid expansion that helped provide health coverage to more than one million people in the two states.

With a House recess approaching and one failed legislative push already in the books, many Republicans believe it's now or never for their promise to tear up the law.

If it fails, MacArthur might be looking at the worst of all worlds: He would be the author of an idea — dubbed "the MacArthur amendment" — attacked for undercutting a well-liked safeguard, but without any tangible results to show for it.

The 56-year-old, two-term congressman from Toms River acknowledged the challenge Tuesday.

"Although you can't escape the politics of this, I try to focus on the actual effect on people, and after 30 years in insurance I read a lot of things that are simply not true about what this bill does and doesn't do," he said off the House floor, surrounded by reporters. "It does protect people with pre-existing conditions, but it does it in a way that doesn't keep everyone else's premiums going through the roof."

His critics, including some Republicans, sharply dispute his assertions. The American Medical Association blasted his proposal Wednesday and the broader repeal bill to which it is attached.

"Proposed changes to the bill tinker at the edges without remedying the fundamental failing of the bill – that millions of Americans will lose their health insurance as a direct result of this proposal," the doctor's group said in a statement.

The impact of MacArthur's amendment is unclear. The Congressional Budget Office, Congress' official analyst, has yet to provide its estimates of the impact.

Upton is a former chairman of the committee that oversees health policy. MacArthur, by contrast, has gained heft in this debate due to his private background, said Rep. Tom Cole (R., Okla.).

"He has, obviously, a professional expertise that far surpasses almost anybody in our Congress," Cole said.

MacArthur founded an insurance company called York Risk Services that made him wealthy before he sold it in 2010 for around $500 million. He also had a daughter, Gracie, who was born with severe health problems and died nearly 20 years ago at age 11.

"If I didn't have insurance, I would be bankrupt, because I also had a child with serious issues and massive medical bills," MacArthur said. "Those are real issues and we have to protect those situations. I believe the bill does that."

His amendment has made MacArthur into a prime political target. A group called "Save My Care" has launched television ads attacking him and on Tuesday the liberal New Jersey Citizen Action delivered a 34,139-signature petition to his South Jersey office urging him to stop his effort.

Facing reelection in a swing district next year, MacArthur has not shied away. He has scheduled a town hall meeting for next week.

MacArthur's deal, which drew conservatives on board with the plan but angered the centrists he normally aligns with, would allow states to opt out of Obamacare's restriction against charging higher rates to people who have pre-existing medical conditions, such as cancer, asthma, or heart disease.

Groups such as AARP and AMA say it could lead to steep price hikes for those people, effectively putting insurance out of reach for people who need it most. They say MacArthur's proposed safeguards would be inadequate.

MacArthur says his plan would reduce costs for healthy people and provide fall-back options for those with pre-existing conditions.

Late-night comedy host Jimmy Kimmel drew national attention to the issue this week with a tearful monologue describing how his son had been born with heart disease and needed surgery to live. Without protections for pre-existing conditions, his son might never be able to obtain health insurance, Kimmel said.

Some Republicans say they should vote for MacArthur's amendment simply to advance the repeal process, hoping the Senate improves the measure -- though the bill, if it passes the House Thursday, will face a difficult road in the closely divided Senate.

"If you kill it in the cradle, you basically are ratifying Obamacare," Cole said.

He said the biggest danger for fellow Republicans is not backing the MacArthur plan, but failing to deliver the promised repeal that energized the GOP base.

"If you think voting no is going to save you in the next election, it's not," Cole said. "We have to do two things: Number one, pass something. Number two: the guys that are designing it … better be right."