Health and Human Services Secretary Sylvia Mathews Burwell warns of damage to the nation’s health care system if the Affordable Care Act is repealed without a replacement plan. (Oliver Contreras/For The Washington Post)

The Republicans’ strategy to repeal the Affordable Care Act risks sending health care in the United States “over a cliff,” the government’s top health official warned Monday as part of an unprecedented campaign by the Obama administration to use its final days to preserve the centerpiece of its domestic legacy.

The stern warning by Health and Human Services Secretary Sylvia Mathews Burwell came on the heels of a journal article and pair of interviews by President Obama himself on the perils of a GOP-controlled Congress deconstructing the sprawling law before defining a sequel. “Suddenly, 20 million people or more don’t have health insurance,” the president said on Sunday on ABC’s “This Week.”

Through its quick succession of assertive messages, the outgoing administration is essentially conceding that the ACA is almost certainly destined for demolition once Donald Trump moves into the White House. Instead of trying to ward that off, Obama and his top aides are seeking to focus public attention on the question of what comes next — and at what cost.

In remarks Monday at the National Press Club, Burwell laid out the administration’s most specific criteria to date for policymakers and consumers to evaluate any health-care plan that a Trump White House or congressional Republicans put forward.

Future approaches to health policy should be judged on whether they provide insurance coverage to as many people as the ACA has, Burwell said, whether they offer the same level of insurance benefits, and whether they continue a trend begun by the 2010 law to slow some medical inflation.

“If it fails on any of these, it’s a step backwards,” she said during what was billed as a farewell speech.

Such admonitions from the highest reaches of an outgoing administration are highly atypical. In their final weeks, most presidents tend to be winding down and helping their successors prepare to assume office.

The last-minute activism reflects “a very unusual set of circumstances, with an incoming Congress beginning the process of trying to dismantle the outgoing president’s signature domestic policy initiative while he’s still in office,” said Larry Levitt, senior vice president of the Kaiser Family Foundation, a health-policy organization. “Perhaps ironically, the timing allows the Obama administration to start to mount a defense of the Affordable Care Act while it still controls the machinery of the government.”

The health-care law, a main whipping post for Republicans ever since it was enacted on purely party-line votes, is the most prominent of a few arenas in which Obama has been writing and speaking lately to try to preserve his administration’s imprint on domestic policy.

In an article published online on Monday in the journal Science, Obama argued for a national policy that embraces renewable energy, rather than the emphasis on fossil fuel production that his successor has promised. Last week in the Harvard Law Review, he touted changes his administration has made to the criminal justice system.

A “perspective” piece by the president on the ACA that appeared Friday in the New England Journal of Medicine was part of this writing spurt. “This approach of ‘repeal first and replace later’ is, simply put, irresponsible — and could slowly bleed the health care system that all of us depend on,” the president contended.

(Daron Taylor/The Washington Post)

“‘Repeal and replace’ is a deceptively catchy phrase,” he stated. “The truth is that health care reform is complex with many interlocking pieces, so that undoing some of it may undo all of it.”

He cited one of ACA’s most popular features, a ban on the once-widespread practice of insurers refusing to cover people who had preexisting medical problems or charging them more. The president-elect and most Republicans in Congress have said they favor preserving the ban. But Obama noted that it would place a large burden on insurers unless they also kept an unpopular aspect of the law requiring most Americans to carry coverage.

Asked by reporters on Monday whether he was concerned about the absence of a replacement plan so far, Trump replied: “Not even a little bit. That’s going to all work out.” The president-elect added, “We’ll be talking about it on Wednesday.” That is when Trump has scheduled his first news conference since July.

The defense efforts by Obama and his top aides parallel the concerns of a growing cadre of medical industry groups, consumers, and a coalition of medical students. They, too, contend that repealing the ACA without a clear new plan would disrupt the health-care system and care for many patients.

A few congressional Republicans have started to express the same view. “We’re possibly creating a boxed canyon for ourself by potentially repealing without replacing,” Sen. Bob Corker (R-Tenn.) told reporters late last week. “I think the vast majority of people believe we’re better off doing both at one time. The question is, can you really make that happen.”

On Sunday, Senate Majority Leader Mitch McConnell (R-Ky.) said Congress “will be replacing [the ACA] rapidly after repealing it.” Speaking on CBS’s “Face the Nation,” McConnell said the Senate intends to take the first step by week’s end by passing a budget resolution that sets in motion procedures to rescind the law. He did not specifically address the budding criticism that Congress should wait to repeal the legislation until a replacement is mapped out, although he said that there “ought not to be a great gap between the first step and the second.”

Pressed to define how long that might be, McConnell replied, “quickly,” without elaborating.

Staff writer Sean Sullivan contributed to this report.