After Republican leaders in Congress failed to destroy the Affordable Care Act last month, President Trump tweeted that the law would “explode.” Now he seems determined to deliver on that prediction through presidential sabotage.

Mr. Trump is threatening to kill a program in the A.C.A. that pays health insurers to offer plans with lower deductibles and out-of-pocket expenses to about seven million lower-income and middle-class people. The president thinks that this will get Democrats to negotiate changes to the 2010 health law. This is cruel and incredibly shortsighted. Without these subsidies, health care would be unaffordable for many Americans, including people who voted for Mr. Trump because they were frustrated by high medical costs.

These subsidies lower the cost of medical care for people who earn between 100 percent and 250 percent of the federal poverty level. For a family of four, that income is $24,600 to $61,500 a year. For example, the deductible on qualifying Obamacare policies for families living at the poverty line in Charlotte, N.C., would be $1,000, compared with $10,000 for a standard policy, according to government data. In Philadelphia a similar family would have no deductible, compared with a $5,000 deductible for policies without subsidies. The government is expected to spend $7 billion on subsidies in 2017, and nearly 60 percent of the 12.2 million people who bought Obamacare policies for 2017 benefit from them.

Conservatives have been trying for years to end these subsidies in an effort to destabilize the A.C.A. House Republicans filed a lawsuit in 2014 to prevent the Obama administration from making these payments to insurers without appropriations from Congress. A Federal District Court ruled in the Republicans’ favor, but President Barack Obama appealed the case and the payments have continued — so far, at least. Mr. Trump has to decide how to proceed.