(Jenny Starrs/The Washington Post)

The “skinny repeal” plan that emerged as Senate Republicans’ best, and perhaps only, strategy for overturning much of the Affordable Care Act would pluck out just a few elements of the sprawling law, but it would pack an outsize punch, causing millions of Americans to lose health coverage and striking fear within the insurance industry.

The plan would remove pieces that lie at the very foundation of the compact the Affordable Care Act has created among the government, insurers, the nation’s employers and the American public.

When the skinny repeal would come to a vote seemed up in the air early Thursday evening. It has been waiting in the wings, a set of ideas that could be introduced as a bill or as an amendment to existing GOP health-care legislation. A congressional budget analysis Wednesday night forecast that the plan would increase the number of uninsured people by 16 million, and health insurance companies warn that it would drive up rates.

In its original form, the central features of the skinny repeal would eliminate the Affordable Care Act’s requirements that most Americans carry health insurance and that employers with 50 or more workers offer them health benefits.

The skinny idea plays off the fact that the insurance requirements, or mandates, are the most unpopular parts of the current health-care law, based on years of public opinion polling. By focusing mainly on those features, plus the elimination of a tax on medical devices, the political strategy behind this narrow bill would be to court Republican conservatives and centrists alike, adopt the measure and then catapult the passed bill into negotiations with the House, which approved its own anti-Affordable Care Act legislation this spring.

However, that path became strewn with doubt early Thursday evening after key Republican senators said they would vote against it unless they had assurance that it would actually lead to a conference committee with the House, where more ideas could be aired — without risk that the plan would simply be approved at the other end of the U.S. Capitol.

Over the course of the day Thursday, “skinny” acquired a few more components, with senators saying the specifics might still change further. The additions included shifting funds from Planned Parenthood — a longtime conservative whipping post — to community health centers and an ill-defined intention to give states more latitude over their Medicaid programs.

Though it would have few provisions, the skinny plan would have big effects.

In a hasty analysis sought by the Senate’s Democrats, congressional budget analysts are estimating that the changes would leave an additional 1 million Americans uninsured this year because consumers would immediately become free to drop coverage. The loss of insurance would quickly swell to 15 million in 2018, mainly among people who buy health plans on their own — the kind of coverage sold through the Affordable Care Act’s marketplaces — or through their jobs.

At the end of the coming decade, 16 million extra people would be uninsured, according to the nonpartisan budget scorekeepers. That is almost three-fourths of the 22 million extra people the analysts predicted would be uninsured under the Better Care Reconciliation Act, the much broader Senate Republican bill that would unwind much of the Affordable Care Act and substitute new policies. The Senate, including nine Republicans, rejected that bill in a vote Tuesday night.

Under the skinny version, the largest additional segment of people without coverage in 2026 would be 7 million who otherwise would be on Medicaid, the public insurance program for low-income Americans. That’s even though the skinny plan would not touch Medicaid’s rules or funding. The broader GOP health-care legislation would reduce Medicaid recipients that year by 15 million. That broader bill would abolish the Affordable Care Act’s expansion and, for the first time in Medicaid’s half-century history, start in a few years to restrict funding for the program as a whole.

For people who buy their own health policies, the skinny plan would cause 5 million fewer Americans to have coverage in a decade — the same as under the broader bill.

The effects that the skinny approach would have on consumers and the business of health care already have drawn scorn from several vantage points.

The left-leaning consumer-health lobby Families USA has branded it a “Frankenstein bill” and said it could lead to a “bait-and-switch” because it could blossom into more profound health-policy changes in House-Senate conference-committee negotiations.

Health insurers are especially worried. As the Affordable Care Act was being assembled, industry representatives agreed to terms uncomfortable for them — such as a ban on charging more to customers with expensive medical problems or denying them coverage — in exchange for the law’s promise that most Americans must have health insurance. In that way, industry leaders reasoned, they would gain millions of healthy new patients whose modest medical expenses would balance out the expense of insuring the sick.

Ever since, the Affordable Care Act’s mandates — or at least strong federal incentives for people to stay insured — have been a bedrock underlying insurers’ willingness to participate in the insurance exchanges, or marketplaces, the law created. On Wednesday, the Blue Cross Blue Shield Association issued a warning. “A system that allows people to purchase coverage only when they need it drives up costs for everyone,” the association’s statement said.

On Thursday morning, America’s Health Insurance Plans, another main industry trade group, echoed those sentiments in its own statement, which alluded to the skinny idea. It said, “Targeted proposals that would eliminate key elements of current law without new stabilizing solutions . . . will not solve the problems in the individual market and, in fact, will result in higher premiums, fewer choices for consumers and fewer people covered next year.”