WASHINGTON — Premiums for the most popular health insurance plans would shoot up 20 percent next year, and federal budget deficits would increase by $194 billion in the coming decade, if President Trump carried out his threat to end certain subsidies paid to insurance companies under the Affordable Care Act, the Congressional Budget Office said Tuesday.

The subsidies reimburse insurers for reducing deductibles, co-payments and other out-of-pocket costs that low-income people pay when they visit doctors, fill prescriptions or receive care in hospitals.

Even before efforts to repeal the Affordable Care Act collapsed in the Senate last month, Mr. Trump began threatening to stop paying the subsidies, known as cost-sharing reductions. He said the health care law would “implode” and Democrats would have no choice but to negotiate a replacement plan. Mr. Trump described his strategy as, “Let Obamacare implode, then deal.”

Those threats continue, though the Trump administration has paid the subsidies each month.

The nonpartisan budget office has now quantified the cost of the threats and potentially handed Democrats a weapon to force Congress and the administration to keep the money flowing.