In the weeks since President Trump’s attempts to replace the Affordable Care Act collapsed, the administration has debated what to do: Try again? Shore up the insurance marketplaces? Or let the whole system collapse?

Mr. Trump has failed to get enough support from his own party, but he hopes to get the Democrats’ help by forcing them to the negotiating table with hints about the chaos he could cause.

His bargaining chip is the government subsidies paid to insurance companies so they can reduce deductibles and other out-of-pocket costs for low-income consumers — seven million people this year.

In an interview with The Wall Street Journal this week, Mr. Trump threatened to withhold the subsidy payments as a way to induce the Democrats to bargain with him.

For now, Democrats are resisting and using his maneuver against him to energize their own party. And they warn that Mr. Trump will be blamed if the insurance markets collapse and people lose coverage next year.

“Republicans are in control of government,” Senator Claire McCaskill, Democrat of Missouri, said Thursday after a town-hall-style meeting in her home state. “If they blow up what access to health care there is right now, they’re going to own it.”

The president’s tone differs from that of Republicans in Congress, who have repeatedly promised a smooth transition away from the law they call Obamacare. “We don’t want to pull the rug out from under people,” the House speaker, Paul D. Ryan, has said.

If the subsidies are interrupted, insurers say, some health plans will increase premiums and others will withdraw from the individual insurance market. That will, in turn, affect millions of other people who do not receive the subsidies.

The issue could come to a head within weeks. When the House reconvenes on April 25, the first order of business will be a spending bill to replace the current stopgap law, which expires three days later. Democrats are determined to put money for the health insurance subsidies into that bill, and some Republicans on the House and Senate Appropriations Committees are open to the idea. But ultimately, the decision will be made by Republican leaders in the two chambers.

If the spending is allowed to continue, the Congressional Budget Office estimates that the federal government will pay $135 billion in cost-sharing subsidies to insurers from 2018 to 2027.

The cloud of uncertainty swirling around the subsidies stems from a court ruling in a lawsuit that House Republicans filed against the Obama administration in 2014. Judge Rosemary M. Collyer of the Federal District Court in Washington ruled last year that spending on the subsidies “violates the Constitution” because Congress never appropriated money for them. She ordered a halt to the payments, but suspended her order to allow the government to appeal.

The Trump administration has not made clear whether it will press the appeal filed by the Obama administration. In a letter to Mr. Trump this week, the U.S. Chamber of Commerce joined the American Medical Association, the American Hospital Association and insurers in seeking “quick action” to guarantee continuation of the subsidies. Without the subsidies, they said, more people will be uninsured and unable to pay medical bills.

Democrats say they will not negotiate with Mr. Trump until he stops his drive to repeal the Affordable Care Act. “President Trump is threatening to hold hostage health care for millions of Americans, many of whom voted for him, to achieve a political goal of repeal that would take health care away from millions more,” said the Senate Democratic leader, Chuck Schumer of New York.