Democrats, eyeing potential turmoil in the run-up to the 2018 midterm elections, have little political reason to cooperate. “One thing is clear,” said the House Democratic whip, Representative Steny Hoyer of Maryland. “House Republicans are going to have to find the votes on their own to dismantle the protections incorporated in the Affordable Care Act that the American people now have.”

A growing chorus of Republican policy experts and senators are pleading to slow the process down or risk a political blood bath.

But Republican leaders and Mr. Trump appear to be laying the groundwork for blaming the law they are annulling for the fallout likely to come in the repeal’s wake.

Mr. Trump asserted on Friday that 2017 would be “a disaster” for the health law. “That’s the year it was meant to explode, because Obama won’t be here,” he said, adding that “as bad as it is now, it’ll get even worse.” On Saturday, he took to Twitter: “ObamaCare is imploding and will only get worse. Republicans coming together to get job done!” And Vice President Mike Pence traveled to Louisville, Ky., on Saturday to assure residents that “the Obamacare nightmare is about to end.”

What is clear is that 2018 — a year that Republicans say will be messy — will loom large for them as they move toward a vote on the measure. But Republicans say that gives them nearly a year of time, since people will experience few changes with their health care in 2017.

Under the proposed House legislation, individuals would no longer be subject to a penalty if they go without health insurance, a politically popular change that would be retroactive to 2016. But they would still enjoy the protections of the Affordable Care Act: Insurers would have to offer a suite of essential health benefits, could not deny them coverage because of pre-existing conditions and could not impose annual or lifetime caps on coverage.

Insurers would be free to raise their premiums to meet these requirements, but because current policies are locked in for the year, voters would not see the effects until 2018. If young, healthy Americans flee the market, freed from the mandate, premiums could soar next year.