The linchpin of House Republicans’ attempt to salvage their health-care legislation is an iffy, “back to the future” idea for dealing with what has been an in­trac­table dilemma: how best to provide insurance to Americans with expensive-to-treat medical problems.

The latest addition to the GOP bill would provide $8 billion over five years to help people with preexisting conditions — including cancer, high blood pressure, asthma and even pregnancy sometimes — afford coverage.

In both substantive and political terms, this amendment is meant to counterbalance Republicans’ previous change to tilt federal health-care policy in a more conservative direction. Last week, to gain support from the chamber’s hard-right faction, the Freedom Caucus, the legislation was altered so that states would be able to circumvent current federal protections that forbid insurers from charging customers with preexisting conditions more than other people.

But that big concession to conservatives — contrary to a promise that President Trump has repeatedly made — prompted jitters from advocates for the elderly and people with serious diseases, as well as from more moderate House Republicans who feared criticism back home.

Backers frame the newest approach as a way to fill in the gap.

(Jenny Starrs/The Washington Post)

Even before the precise language was released Wednesday night, leading health policy experts said the amendment raises big questions about how — and how well — it would work in practice. Among the most significant: How many states would back away from the federal protections for people with medical conditions? And how many of those people would lose their coverage because of other changes in the House plan?

“Does it really guarantee that all individuals who have preexisting conditions will be able to find insurance at affordable rates?” said Dan Mendelson, president of Avalere Health, a Washington-based consulting firm.

The scramble on Capitol Hill over preexisting conditions is the most recent twist in a debate that has daunted and divided policymakers for years.

There is no one single meaning of “preexisting conditions,” but the term generally refers to acute or chronic ailments that a person has or had in the past and that might return. In addition, such ailments require more medical care than healthy people tend to use. Before the 2010 Affordable Care Act, the law that Trump and congressional Republicans are eager to dismantle, Americans with such medical challenges often could not get or afford insurance.

An estimated 50 million to 129 million Americans have some preexisting health problem, according to an analysis by federal health officials during the Obama administration.

At the heart of the debate is whether it is better for the sickest people to be part of the same insurance pool as healthier people or whether it is better to separate them out. In prohibiting insurers to charge more to people who were sick, the ACA combined everyone in the same risk pool. The newest House amendment is part of a pre-ACA tradition of trying to help people largely by creating special insurance for them.

Specifically, the provision would require a “risk-sharing plan” of any state applying to the Department of Health and Human Services for a permission to return to letting insurers charge high prices to customers with medical problems. That plan could take different forms. States could use their funding allotment to create “high-risk pools,” for example, returning to a strategy more than half the states tried before the ACA. Others could use the money as subsidies to lower insurance premiums for eligible people.

(Jenny Starrs/The Washington Post)

According to the amendment, the $8 billion would become part of a “Patient and State Stability Fund” envisioned by the GOP plan. The money would be for people who buy coverage individually, rather than through a large or small employers. Insurers could not raise rates for current customers, so the money would only help people who go uninsured for about two months — the same time frame as another aspect of the GOP legislation that would allow insurers to impose surcharges for people with that coverage cap. Under the bill, higher rates for preexisting conditions could last one year.

That money would add to the $100 billion fund, which is intended to last through 2026, plus $15 billion recently proposed to try to lower insurance costs.

A Republican House aide familiar with the amendment, who spoke on the condition of anonymity, portrayed the people who would need the extra help as “a small, narrow group.”

However, Larry Levitt, senior vice president of the Kaiser Family Foundation, said that the number of Americans with medical conditions and no insurance could increase under the GOP plan because the ACA’s subsidies would be replaced by smaller, more restrictive ones.

And, Levitt said, it is impossible to anticipate how far the amendment’s money would have to stretch without knowing how many states would try to get rid of the current insurance rules. It is also unclear what would happen once the money was gone in five years.

Robert Graboyes, a senior research fellow at George Mason University’s Mercatus Center, called the $8 billion “a pittance” and said previous high-risk pools have tended to run out of money. “Promising we are going to cover everyone with preexisting conditions is kind of a heartwarming thing to say. But . . . either you fund it, or you don’t make the promise.”