The number of people without insurance would jump by 18 million within a year or so, and 32 million within a decade. Premiums would go up by 20 percent to 25 percent right away; by 2026, they’d be double what they would be under current health care law.

Such are the likely consequences of passing legislation that Senate Majority Leader Mitch McConnell (R-Ky.) says he intends to bring to a vote, now that the Republican Party’s effort to craft a replacement for the Affordable Care Act has fallen apart.

The bill is actually an old piece of legislation ― a 2015 proposal to repeal large swaths of “Obamacare” in two steps. It would immediately end the individual mandate, which is the penalty for people who don’t get insurance. Two years later, it would eliminate new tax credits for people who buy coverage on their own and cut off extra federal matching funds for expanding state Medicaid programs.

For that reason, the bill has come to be known as “repeal-and-delay.”

The legislation would leave in place a set of consumer protections ― including guarantees of coverage for people with pre-existing conditions ― that are among the law’s most popular provisions but also drive up premiums. Republicans have pointed to these elements as their chief criticisms of the 2010 health care law.

Maintaining the protections was a nod to the rule of the budget reconciliation process, which would allow Republicans to pass their bill with a simple majority.

Republicans promised that their scheme would promote a “stable transition” to a new system ― a vow McConnell made again on Tuesday morning, while speaking on the Senate floor.

But when the Congressional Budget Office examined the proposal, it concluded that the combination of keeping those protections in place and eliminating the mandate and then the subsidies for buying private insurance would wreak havoc with insurance markets.

Carriers, rightly fearful that their risk pools would tilt toward sicker and sicker customers, would jack up premiums in response ― making coverage unaffordable for many. The problem would hit quickly, because the individual mandate penalty is a major incentive for healthy people to get coverage. (Whether it happened in the next calendar year or the subsequent one would depend on whether insurers had enough time to reset their rates.)

Markets would deteriorate further over time, the CBO predicted. And all of this would happening against a backdrop of deep cuts to Medicaid, as the federal government yanked back the money that’s made it possible for 31 states and the District of Columbia to widen eligibility for the program.

In those states, anybody in a household with income below or just above the poverty line now qualifies for Medicaid, helping to bring the number of Americans without insurance to historic lows. Medicaid has become particularly vital for battling opioid addiction in states like Ohio and West Virginia ― whose GOP senators, not coincidentally, have been among the most anxious about proposed Medicaid cuts in repeal legislation.

CBO predictions are subject to same considerable uncertainty as all predictions about health insurance markets. But the agency’s findings were consistent with what other independent analysts, including those at the Urban Institute, had concluded.

Aaron Bernstein / Reuters

If McConnell proceeds with his plan to bring up the 2015 legislation for a vote, he will be carrying out a strategy that GOP leaders discussed at length ― and then dropped ― after Donald Trump was elected president.

At the time, passing the 2015 proposal or something close to it seemed like the most straightforward way to repeal the Affordable Care Act, if only because the legislation already existed and both houses had already voted for it. But Republicans voted for that bill, knowing all along that then-President Barack Obama would veto it.

The prospect of passing that bill with a president ready to sign it clearly spooked not just the public but even some Republicans, because there was no guarantee that an alternative would fulfill GOP promises of better, cheaper coverage ― or whether Republicans could even agree on a replacement at all.

That danger would seem to be even greater now that McConnell has admitted he can’t get his members to vote for a bill, despite spending seven months trying to write one.