WASHINGTON – Thwarted over and over in his effort to repeal and replace Obamacare by a unified Democratic Party and a handful of Republicans, President Trump is using his executive power to at least partially fulfill his major campaign promise.

Trump plans to halt payments to insurers under the Affordable Care Act "immediately," in a major blow to Obamacare that is likely to draw a legal challenge.

The president used the overnight decision to ramp up pressure on Democrats to negotiate a "fix" to the "imploding" health-care law.

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"The Democrats ObamaCare is imploding. Massive subsidy payments to their pet insurance companies has stopped. Dems should call me to fix!" he said in a pre-dawn tweet on Friday.

He added, "ObamaCare is a broken mess. Piece by piece we will now begin the process of giving America the great HealthCare it deserves!"

The Justice Department immediately notified a federal appeals court in Washington, D.C., in connection with a related lawsuit, that an upcoming Oct. 18 payment “will not occur," reported Fox News.

The White House said in a statement that the Department of Health and Human Services has determined there is no appropriation for so-called cost-sharing reduction payments to insurers under the Obamacare law.

"We will discontinue these payments immediately," said acting HHS Secretary Eric Hargan and Medicare administrator Seema Verma.

In California, the state attorney general Xavier Becerra said he was prepared to sue the Trump administration to protect the subsidies. Eric Schneiderman, the attorney general of New York state declared he would “not allow President Trump to once again use New York families as political pawns in his dangerous, partisan campaign to eviscerate the Affordable Care Act at any cost."

The president is dismantling his predecessor's signature health-care legislation with the "power of the pen," providing "millions of Americans with Obamacare relief."

The attack on the federal subsidies came as a double blow to Obamacare, just hours after Trump issued an executive order to allow small businesses and individuals to band together, creating so-called "health-care associations," and purchase insurance across state lines.

The move, he said, will increase competition and bring down costs, making it easier for people to buy cheaper, bare-bones health insurance.

"We aim to allow more small businesses to form associations to buy affordable and more competitive health insurance. This will open up additional options for more [employers] to buy health care plans their workers want," Trump explained at a White House event marking the action.

"This will create tremendous competition — the competition will be staggering," he said.

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"Insurance companies will be fighting to get every single person signed up," he continued. "And you will be, hopefully, negotiating, negotiating, negotiating. And you'll get such low prices for such great care. It could have been done a long time ago and should have been done a long time ago."

Democrats have turned the American health care system into a "nightmare," Trump said.

"Seven years ago, congressional Democrats broke the American health-care system by forcing the Obamacare nightmare onto the American people," he said. "It's been a nightmare — you look at what's happening to the premiums and the increases — 100 percent, 120 percent, one case — Alaska — over 200 percent."

The Democrats have been unanimous, first in adopting Obamacare and, since Trump was elected, in opposing any changes.

Joining them have been three GOP lawmakers, Sens. John McCain of Arizona, Susan Collins of Maine and Lisa Murkowski of Alaska.

"Now every congressional Democrat has blocked the effort to save Americans from Obamacare, along with a very small, frankly handful of Republicans — three — and we're going to take care of that also," he said.

The executive order, Trump said, directs the Labor, Treasury and Health and Human Services Departments to reinterpret alternative offerings, with the aim of expanding coverage options for consumers.

While the Obama administration limited the length of short-term insurance policies to three months, the Trump administration intends to restore insurers' capacity to sell short-term policies that allow up to a year of coverage.

"The Department of Health and Human Services, the Treasury and the Department of Labor will take action to increase competition, increase choice and increase access to lower priced, high quality health-care options. And they will have so many option," the president said. "This will cost the United States government virtually nothing and people will have great, great health care, and when I say people I mean by the millions and millions."

Broader access to so-called association health plans, or AHPs, has been promoted by Sen. Rand Paul, R-Ky.

Paul appeared at the White House ceremony with Trump after working with the president for months on the order.

The Republican opposed the Senate’s most recent attempt to overhaul Obamacare because he said it left too many of the law’s regulations and spending programs in place.

"President Trump is doing what I believe is the biggest free-market reform of health care in a generation," Paul said during a signing ceremony in the White House Roosevelt Room. "This reform, if it works and goes as planned, will allow millions of people to get insurance across state lines at an inexpensive price."

Trump acknowledged that given what happened with the debate on health-care reform since he's been in office, fully repealing Obamacare be a long fight.

But repeal needs to be the long-range goal, policy experts contend.

Robert Graboyes, a senior research fellow and health care scholar at George Mason University's Mercatus Center, explained insurance companies already market in multiple locations by getting licensed in different states, as the Blue Cross companies do.

"It's unlikely to have really any significant impact. … It's certainly not something that's going to be a tremendous cost-saver to do so," he claimed.

Rep. Mo Brooks, R-Ala., contends the president's executive action does not begin to adequately overhaul Obamacare, "but it is incremental progress."

"Competition is always a good thing. Sometimes competition has a major impact on pricing. Sometimes it has a minor impact on pricing. But it always has a positive impact for consumers," he said.

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Senate Minority Leader Chuck Schumer accused Trump of “using a wrecking ball to single-handedly rip apart our health-care system.”

“Having failed to repeal the law in Congress, the president is sabotaging the system,” Schumer said.

Trump said the order was “only the beginning” and that his administration would take additional actions. He said he would “pressure Congress very strongly to finish the repeal and the replace of Obamacare once and for all.”

Meanwhile, congressional Republicans on Thursday swore they weren't done trying to repeal Obamacare after Trump signed an executive order borne out of frustration over Congress' inability to eliminate the law.

"I will continue to push for our legislation which will return healthcare power and decision-making to patients and states," Sen. Lindsey Graham, R-S.C., said after Trump signed the order Thursday.

Rep. Mark Meadows, R-N.C., the leader of the conservative House Freedom Caucus, said Trump's order is a step in the right direction, reported the Washington Examiner.

"Congress would do well to follow the president's lead and renew our push to keep our seven-year promise to repeal and replace Obamacare," he said. "Failure on that end should not be an option."