WASHINGTON — So what, exactly, is Tom MacArthur proposing?

The Republican Congressman from South Jersey has thrown himself into the middle of the heated fight over the Affordable Care Act, helping revive the GOP's repeal plan with a proposal that has won over conservative holdouts, but could scare away moderate votes.

Among them is Rep. Pat Meehan, of Delaware County, who said Thursday he will oppose the latest plan, joining every GOP Congressman from the Philadelphia region, save for MacArthur.

In a statement to the Inquirer Meehan said the bill "threatens to send premiums skyrocketing for people with pre-existing conditions. It will make coverage more expensive for older Americans as they near retirement. And it threatens essential healthcare benefits like doctor's office visits, opioid addiction treatment and emergency room care."

Rep. Ryan Costello, of Chester County, also came out against the bill, criticizing changes that would affect people with pre-existing conditions. "I remain a no vote on this bill in its current form," said a statement.

As of Thursday afternoon they were two of 19 declared Republican opponents, according to a The Hill. The GOP can afford only 22 defections.

Here are key questions and answers about who the bill might help and hurt, and how it might affect the repeal push.

The background 

MacArthur's proposal is an add-on to the repeal bill Republicans offered in March and abruptly pulled back when support collapsed. That plan was intended to undo many of the mandates in former President Obama's signature health law, which critics say raised prices and intruded on health care.

Nonpartisan analysts estimated that it would increase the count of uninsured Americans by 24 million over a decade. In Pennsylvania and New Jersey there were concerns that it wouldroll back a Medicaid expansion that helped more than 1 million people in the two states.

What’s he proposing?

He offered two major changes to woo conservatives. Both would roll back Obamacare consumer protections, the better, he and his new allies argue, to lower prices and increase flexibility.

One would scale back rules protecting people with pre-existing medical conditions like cancer, asthma, obesity or those who were pregnant.

Before the law was passed, those people often found it impossible to buy insurance. In Pennsylvania, 5.3 million people under the age of 65 had a condition that could make them uninsurable, according to the liberal Center for American Progress. In New Jersey it was 3.8 million.

Obamacare requires insurers to offer them coverage at similar rates to those who are healthy. Even many critics of the law pledged to keep this popular change.

MacArthur's plan, though, would let states opt out of the provision. Healthy Americans would likely pay less: They'd no longer help offset the costs of those with serious medical needs. And insurers, MacArthur stresses, would still be required to offer coverage to everyone.

The American Medical Association, in a letter to House leaders Thursday, called MacArthur's assurances "illusory."

With insurers free to set prices as they like, the costs would likely be exorbitant for people with serious needs, the AMA argued.

MacArthur's office noted that the plan would not allow such rate hikes for people who have insurance and stay insured. He also offers a safety net: states that erase the mandate would have to set up a "high risk pool" for those shunned by insurance companies. His plan includes $130 billion to bolster those pools.

What else changes?

MacArthur would also let states get waivers for "essential health benefits."

Under Obamacare, insurance plans are required to cover certain benefits, including maternity care, substance abuse treatment and prescription drugs. The idea was to wipe out flimsy plans that left people facing big bills for critical services.

MacArthur would let states get waivers to opt out of this requirement, though he said rules barring gender discrimination would remain in force.

In practice, the change would still lead to higher costs for some groups, including women, said Larry Levitt, senior vice president of the health policy group the Kaiser Family Foundation. That's because with maternity care, for example, no longer required, insurers could make people pay more for that service.

Would everyone be affected?

People who have insurance through their employers would likely not feel the change, MacArthur's office argues. It said the changes would affect roughly 7 percent of people who buy their insurance individually or in small group plans.

Still, the changes worry some critics who say they open the door to going back to the old ways of treatment for people with pre-existing conditions.

Can the House plan pass now?

With more conservatives on board, Republicans look closer to the 216 required votes, but they might lose too many centrists.

No vote is scheduled, for now, but Republican leaders are hopeful they could pull one together soon, perhaps even this weekend or next week.

What about the Senate?

Republicans have an even narrower margin in the Senate and several lawmakers there have raised concerns about the plan.

That only aggravates centrists: rank-and-file lawmakers might be forced to cast a controversial vote for an idea that could die a quick death. (Democratic House leader Nancy Pelosi said Thursday that a vote for the bill would leave Republicans with "doo doo on their shoes.")

Rep. Charlie Dent, an Allentown Republican, accused conservatives of supporting the bill only to make moderates into the new scapegoats for a repeal failure.

MacArthur argues that if Republicans can move the process along and get some bill, any bill, through the Senate, they'll be on the brink of finally delivering on their promise to repeal Obamacare.​