Although House Speaker Paul D. Ryan (R-Wis.) acknowledged Friday that “Obamacare is the law of the land,” its survival or collapse in practical terms now rests with decisions that are in President Trump’s hands.

In the coming weeks and months, the White House and a highly conservative health and human services secretary will be faced with a series of choices over whether to shore up insurance marketplaces created under the Affordable Care Act — or let them atrophy. These marketplaces are currently a conduit to health coverage for 10 million Americans, but they have been financially fragile, prompting spiking rates and defections of major insurers.

In an interview on Friday with The Washington Post, Trump made his inclinations clear: “The best thing politically is to let Obamacare explode.”

The president said that the law remains “totally the property of the Democrats” and that “when people get a 200 percent increase next year or a 100 percent or 70 percent, that’s their fault.” Former Obama administration officials countered that Trump and congressional Republicans are responsible for what happens next.

In the seven years since a Democratic Congress passed the law, public sentiment over it has been closely divided. Support has grown slightly in recent months as Republicans tried to begin dismantling it.

(Peter Stevenson/The Washington Post)

There are many levers within the ACA that the administration could use to undermine the law or, instead, try to stabilize its marketplaces. In addition, federal rules could be redefined, giving the government’s health policies a more conservative twist even with the law still in effect.

According to health-care experts from across the ideological spectrum, an imminent question is whether the political tumult surrounding the ACA’s fate and the president’s talk of explosion could further shake the confidence of consumers and insurers alike. Doing so could prompt exits from the marketplaces.

Trump’s threat could become “a self-fulfilling prophecy,” said Andy M. Slavitt, the acting administrator of the federal Centers for Medicare and Medicaid Services for the last two years of the Obama administration. “That’s like inheriting an overseas war, and deciding you let your own soldiers get killed because you didn’t elect to enter that war.”

Mario Molina, chief executive of Molina Healthcare, a small company covering about a million Americans through the ACA’s insurance exchanges, said he is unsure whether it will lessen its participation. Its decision this spring will hinge on actions by the White House and GOP lawmakers, he said. “The ball’s sort of in their court. The choices they make are going to determine what happens to the marketplace.”

The decisions facing the administration are, in essence, a sequel to an executive order the president issued his first night in office, when he directed federal agencies to ease the regulatory burden that the ACA has placed on consumers, the health-care industry and health-care providers. So far, the main action stemming from that directive is a move by the Internal Revenue Service to process Americans’ tax refunds even if they fail to submit proof that they are insured, as the ACA requires.

But there are other steps the administration could take. A major one would be to end cost-sharing subsidies the law provides to lower- and middle-income people with marketplace plans to help pay their deductibles and co-pays. Those subsidies, which would have been erased by the House Republicans’ bill, are the subject of a federal lawsuit.

Another question is how the administration will handle the next enrollment season for ACA health plans, which will begin in November. The end of the most recent season coincided with Trump’s first days in office, and the new administration yanked some advertising meant to encourage sign-ups — possibly resulting in a small dip in enrollment by the final deadline.

View Graphic Which Republicans forced Trump to pull the health-care bill

And while a set of federal essential health benefits, required of health plans sold to individuals and small businesses, will now remain in law, federal health officials could narrow what they require, limiting prescription drugs, for instance, or the number of visits allowed for mental-health treatment or physical therapy.

The administration also could take advantage of a part of the ACA that, starting this year, lets health officials give states broad latitude to carry out the law’s goals — including more free-market approaches that conservatives favor. Health and Human Services Secretary Tom Price and other top agency officials already have signaled they would allow states to impose work requirements on able-bodied adults to qualify for Medicaid — something Obama officials steadfastly rejected.

“The administration could do everything from actively undermining the law to trying to reshape it to moving it in a more conservative direction,” said Larry Levitt, senior vice president of the Kaiser Family Foundation.

The question of whether the ACA’s marketplaces can or should be strengthened is a matter of considerable debate. In comparing the House GOP bill with the ACA, congressional budget analysts concluded this month that the insurance market for people who buy coverage on their own “would probably be stable in most areas” either way.

During an afternoon news conference shortly after withdrawing the Republican legislation, Ryan reiterated his oft-stated contention that the marketplaces are beyond repair. He briefly suggested, however, that perhaps the Trump administration could improve their stability.

Chip Kahn, president and CEO of the Federation of American Hospitals, said that policymakers must find a way to shore up the marketplaces because a broad swath of Americans rely on them. “There always has been an individual market made up of entrepreneurs who own small businesses, and farmers and ranchers, and it’s sort of mandatory that there be policies available to them,” Kahn said.

House Republicans were notably silent on Friday about the prospects of further work on health policy. A few senators sounded more hopeful that efforts to improve the law would continue.

Sen. Bill Cassidy (R-La.) said in an interview that he disagreed with Trump’s assertion that letting the markets explode would be the best course of action. “I hope that doesn’t have to happen,” said Cassidy, co-sponsor of a separate bill that would preserve the ACA but tip more latitude to the states.

Harvard University economics professor David Cutler, who helped advise the Obama White House on health care, challenged Trump’s argument that the ACA will always be associated with Democrats. “He owns it now,” Cutler said in an email, “because he could take many steps to stabilize things.”

Carolyn Y. Johnson contributed to this report.