President Trump touted his executive order on ObamaCare that attempts to lower premium costs for younger Americans and others while cutting off federal subsidies to insurance companies, saying their “windfall” has ended.

“Health Insurance stocks, which have gone through the roof during the ObamaCare years, plunged yesterday after I ended their Dems windfall!” Trump tweeted Saturday morning.

Trump argues the executive order he signed Thursday will give millions of Americans more access to affordable health insurance, essentially by allowing them to buy premiums through large-group programs.

“Very proud of my Executive Order which will allow greatly expanded access and far lower costs for HealthCare. Millions of people benefit!” Trump said in a second early morning tweet.

A separate decision issued by the Trump administration Thursday night cuts billions in federal dollars to insurance companies that are used to subsidize consumer costs -- lowering out-of-pocket expenses like co-payments and deductibles for low- and middle-income customers. About 6 million Americans benefit from the subsidies.

Trump and others consider the money a windfall for the companies. However, critics argue that ending them would drastically increase premium costs for millions of Americans because insurers under the 2010 health care law known as ObamaCare are required to lower costs for poorer customers.

So as a result of subsidies cut, carriers are likely to recoup the lost money by increasing premiums for people buying their own health insurance policies.

The National Association of Insurance Commissioners estimates that Trump's move would produce a 12 percent to 15 percent upsurge in premiums.

Congressional Democrats, convinced they have important leverage, promised to press for a bipartisan deal to restore the money by year's end. That drive could split the GOP. On one side: pragmatists seeking to avoid political damage from hurting consumers. On the other: conservatives demanding a major weakening of the Affordable Care Act as the price for returning the money.

"The American people will know exactly where to place the blame," declared Senate Minority Leader Chuck Schumer (D-N.Y.), all but daring Trump to aggravate what could be a major issue in the 2018 congressional elections.

Trump acted after the GOP-run Senate failed this summer to repeal and replace ObamaCare, one of his major campaign promises.

The president has long derided the subsidies as bailouts to insurers, even though the payments and the cost reductions for consumers are required by law.

A federal judge has found that Congress never properly approved the payments. The subsidies have continued under Obama and Trump until now, despite prior Trump threats to block them.

The Associated Press contributed to this report.