But, of course, there is a downside.

The individual mandate is unloved because no one likes being told what to do. But many independent analysts have concluded that, without a mandate, health insurance would become more expensive and cover fewer people. With the nudge of a mandate, more healthy people tend to buy insurance, reducing the average cost of coverage. Without one, the theory goes, mostly sick people buy insurance, and premiums rise to cover that sicker pool.

Fewer people would probably be covered under Medicaid, too. Over the last few years, signups for Medicaid have increased substantially, even among people who could have been covered before Obamacare expanded eligibility. Many of those people presumably didn’t realize they qualified for Medicaid and first tried to buy private insurance because of the mandate, before learning that they could get Medicaid and not have to pay a premium. Without a mandate, fewer people are likely to find their way into the program.

The Congressional Budget Office thinks that eliminating the individual mandate would have substantial negative effects on the insurance market, raising prices and reducing enrollment. It is hard to imagine that more insurers would wish to participate in this smaller, sicker market. The budget office still needs to evaluate a skinny repeal bill, but it seems likely that the reductions in coverage from a mandate repeal would save the federal government enough money for the bill to comply with budget instructions.

It is worth considering these effects in the context of Republicans’ criticisms of Obamacare itself. On the Senate floor Tuesday, Mr. McConnell assailed the health law as building unstable insurance markets and providing too little consumer choice. A skinny repeal would probably exacerbate those effects.