“If you want to be involved in the exchanges and you lose money, the American taxpayer should not have to bail you out,” Mr. Rubio said on the Senate floor on Thursday.

A White House spokeswoman, Katie Hill, declined to offer the administration’s position on proposals that she said were still theoretical. “We are not going to weigh in on the possible inclusion of proposals floated by members of Congress” in potential legislation, she said.

Congress established the program in 2010 to protect insurers against the uncertainties they faced in setting the level of insurance premiums when they did not know who would sign up for coverage under the Affordable Care Act. Under the law, the federal government shares risk with insurers, limiting their gains and losses on insurance sold in the public marketplaces from 2014 through 2016. If consumer payments to an insurer exceed the company’s medical expenses by a certain amount, the insurer pays some of that profit to the government. But if premium payments fall short of medical expenditures by a certain amount, the insurer is eligible for payments from the government.

The hope was that payments into the program would be in balance with payments out, shielding taxpayers from responsibility.

Mr. Rubio latched on to the issue in late 2013, recognizing not only the importance of risk corridors to the operation of the Affordable Care Act but also the political potency of a program he labeled crony capitalism — putting taxpayers “on the hook for Washington’s mistakes,” as he said when he reintroduced his risk corridor bill in January.

The “bailouts” of big banks and other financial firms during the economic crisis of 2008 and the rescue of the Big Three automakers that year and the next remain politically unpopular.

Then the numbers rolled in from the insurance exchanges’ first year of operation: Losses were so steep that insurance-company requests for risk corridor payments were $2.9 billion, compared with only $362 million paid into the program by profitable plans.