President Trump’s decision Thursday to cut off crucial health-care subsidies has once again revived the long-running debate over the Affordable Care Act, increasing the potential for a government shutdown in December and making the issue central in next year’s midterm elections.

The move to end insurer subsidies could propel premiums an average of 20 percent higher next year for those who purchase insurance on the individual market, according to a nonpartisan congressional analysis.

Trump and Republican allies defended the move as removing a giveaway for insurance companies, and they blame rising premiums on fundamental flaws in then-President Barack Obama’s signature health-care reform law. But Democrats called it an act of sabotage against the ACA for which the GOP will be held responsible at the polls.

The dispute sets the stage for another wave of political battles over the nation’s health-care system, as Republican lawmakers will need to decide whether to authorize the subsidies through legislation as well as whether to once again attempt a broader repeal of the ACA, popularly known as Obamacare. Democrats could also use a Dec. 8 appropriations deadline to threaten a government shutdown if the subsidies are not restored.

The party’s leaders stopped short of such a threat Friday. But Democrats warned more broadly that escalating Republican efforts to undermine the ACA — which also included an order by Trump on Thursday loosening insurance requirements — would be used against the GOP in the 2018 elections.

How the Trump administration is undermining the ACA

“Republicans in the House and Senate now own the health-care system in this country from top to bottom, and their destructive actions, and the actions of the president, are going to fall on their backs,” Senate Minority Leader Charles E. Schumer (D-N.Y.) told reporters Friday. “The American people will know exactly where to place the blame when their premiums shoot up and when millions lose coverage.”

Democratic campaigns immediately seized on Trump’s move to undermine the ACA, blasting supporters within hours with emails asking them to sign petitions.

“He’s willing to let people die if it means he can claim a big political win,” said a message from the Democratic National Committee. “Call it craven, call it heartless and cruel. But don’t let this moment pass you by.”

But Corry Bliss, the executive director of the Congressional Leadership Fund, a super PAC that plans to spend more than $100 million over the coming year to keep the House in GOP hands, said he expects the issue to have minimal bearing on the midterms.

“One party is trying to cut middle-class taxes, the other party is trying to raise taxes and increase spending by trillions,” Bliss said, referring to tax overhaul that Republicans are hoping to pass. “That is and will be the most important issue of 2018.”

Bipartisan health talks are underway in the Senate, led by Sens. Lamar Alexander (R-Tenn.) and Patty Murray (D-Wash.), respectively the chairman and ranking Democrat of the Health, Education, Labor and Pensions Committee. Those talks could include a continuation of the subsidy payments.

Senate aides said Friday that the talks are continuing and that a deal between the two could be within reach. But it is unclear whether Republicans at large would accept any deal the pair might strike — a reality highlighted Friday by remarks that White House budget director Mick Mulvaney made to Politico, indicating that Trump would not support a "clean Murray-Alexander bill."

“The president has said pretty clearly that he’s willing to talk to just about anybody about repealing and replacing [Obamacare],” Mulvaney said. “But if the straight-up question is: Is the president interested in continuing what he sees as corporate welfare and bailouts for the insurance companies? No.”

Trump’s decision to act on health care comes two weeks after the expiry of a key deadline. Before the deadline, Senate Republicans, using special budget procedures, could have passed a health-care bill with 50 senators’ votes plus the vice president’s.

Republicans could add similar instructions to their next budget, which is expected to be on the Senate floor next week, but party leaders have so far kept the framework focused on a major tax overhaul that is at the center of the GOP agenda.

The White House held off for months on issuing regulations addressing health care in hopes that Congress would pass legislation to replace parts of the ACA. But after the budget deadline passed, the administration decided to move forward with the regulatory efforts.

The subsidies had been a source of debate inside the White House, with aides including former Health and Human Services Secretary Tom Price arguing in favor of continuing the payments until Congress acts.

But the president, backed by other aides, including Mulvaney and Vice President Pence, leaned against the idea from the beginning, arguing that the payments only boost private insurance companies’ profits.

“That money is a subsidy for insurance companies,” Trump told reporters outside the White House on Friday. “Take a look at their stocks. Look where they are. They’re going through the roof.”

Ultimately, people familiar with the discussions said that the White House hopes to revisit the repeal-and-replace effort in January or February — after Congress tackles tax legislation — in an effort to prevent vulnerable lawmakers from having to run for reelection without fulfilling a signature promise.

“It’s something they will do on a short-term basis and then come back at the larger issue,” said Grace-Marie Turner, president of the Galen Institute, a conservative health-policy organization. “There are a lot of members who are worried about being primaried, so they need something to run on.”

Democrats, however, said they would try to force the subsidy payments to be paid before then. Current federal appropriations expire Dec. 8, and Democrats could threaten to withhold votes on any extension unless the issue is addressed, threatening a government shutdown.

Schumer declined to draw a hard line when asked whether Democrats would oppose any spending bill that did not include the cost-sharing payments. “I think we’re going to have a very good opportunity . . . to get this done in a bipartisan way, if we can’t get it done sooner,” he said.

House Minority Leader Nancy Pelosi (D-Calif.), in an interview, made a starker declaration about the cancellation of the subsidies: “We have to try to put a stop to that immediately, these particular pieces of it, because people will die.”

Democrats can block any spending bill from passage in the Senate, where a 60-vote supermajority is needed to pass most major legislation. In the House, Democrats have frequently provided the majority of the votes for bills keeping the government open — giving them significant leverage should they choose to use it.

Rep. Joseph Crowley (D-N.Y.), chairman of the House Democratic Caucus, said Friday that continuing the health-care payments was already high on the party's list of demands going into the last spending negotiation last month.

"It was a priority then, it's a priority now, and it will be a priority in the future as well for us," he said. "What will help the Affordable Care Act work is stability, and what the president is doing is to purposely destabilize the system. . . . It's a willful act of sabotage."

Key conservatives, meanwhile, warned that any attempt to continue the subsidies, which were expected to total about $7 billion this year, would be met with fierce resistance.

Rep. Mark Walker (R-N.C.), chairman of the conservative Republican Study Committee, said the only way he and other GOP conservatives could stomach an extension would be as a bridge to a new, more conservative health-care system.

Trump’s move to end the subsidies and make other changes to health insurance markets by executive action, he said, could create new momentum for the type of health-care overhaul that Republicans have thus far failed to move through the Senate.

“This may create enough energy and buzz to say, ‘Okay, we’ve got to get back to the drawing board and do something pretty quick here,’ ” he said.

Passing any significant legislation that advances the Republican health-care agenda is likely to be impossible under normal Senate rules, which would require at least eight Democrats and independents to break ranks if all 52 Republicans agree on a health bill.

Besides the talks between Alexander and Murray, a parallel effort is underway among conservatives to forge a bill that might include continuing the subsidy payments, Rep. Mark Meadows (R-N.C.) said in a Friday interview, citing talks with Sen. Ron Johnson (R-Wis.) and other GOP senators. But any deal, Meadows said, would have to include significant changes to expand health-insurance options beyond what the ACA currently allows — including some changes Democrats have fiercely opposed.

"We need to fundamentally address some of the other issues that are increasing premiums," said Meadows, chairman of the hard-right House Freedom Caucus. "Bailing out insurance companies is not a wonderful conservative talking point, and if that's all it is . . . then it's not going to be met with great receptivity" among Republicans.

Abby Phillip contributed to this report.