This would not be devastating to most of the people who use exchanges, because they receive federal subsidies that limit how much they have to pay. But it could really hurt middle-class families who earn too much to qualify for government assistance (about $82,000 for a family of three) and are already facing big premium increases. People in this group would have the terrible predicament of spending a lot of money buying health insurance or taking a chance by buying a skimpy temporary plan, hoping that nobody in the family gets sick or injured.

This proposal is the latest in a series of steps the administration has taken to weaken the A.C.A. and the health care system. In January, it proposed allowing employers and sole proprietorships to form associations for the purpose of buying insurance policies that do not have to comply with the protections of the A.C.A. And it recently began allowing states like Kentucky to take Medicaid benefits away from people who are not employed, creating a system of red tape intended to hurt poor people who have lost their jobs or are unable to work.

If the administration were actually serious about reducing health care costs, it would try to improve the A.C.A., not dismantle it. For example, President Trump could work with Congress to offer subsidies to middle-class families who do not qualify for help under Obamacare. Or he could push for the creation of a national reinsurance program that would encourage insurers to offer policies in more parts of the country at lower costs by protecting them against steep losses from very sick patients.

But Mr. Trump and his Republican allies in Congress seem unwilling to pursue constructive health care policies because they are obsessed with undoing Obamacare. Regrettably, the cost for their rage will be the health care of millions of low-income and middle-class families.