U.S. President Donald Trump on Friday pledged to dismantle Obamacare “step by step” after he scrapped subsidies to health insurers that help low-income Americans pay out-of-pocket medical expenses, a move that raised concerns about chaos in insurance markets and could face legal challenges. Trump’s action, announced late on Thursday, took aim at a critical component of the 2010 law, his Democratic predecessor Barack Obama’s signature domestic policy achievement. Frustrated by the failure of his fellow Republicans who control Congress to repeal and replace Obamacare, Trump has taken this and several other steps to chip away at it. The administration will not make the next payment to insurers, scheduled for Wednesday, Attorney General Jeff Sessions said. The subsidies cost $7 billion this year and were estimated at $10 billion for 2018, according to congressional analysts. Trump’s action came just weeks before the Obamacare open enrollment period begins on Nov. 1 for 2018 insurance policies through the law’s marketplace. Congressional Democrats accused Trump of sabotaging the law, and Democratic state attorneys general in New York and California threatened a legal challenge. Hospitals, doctors, patient advocates and health insurers decried Trump’s move, saying consumers will ultimately pay the price. They called on Congress to appropriate the funds needed to keep up the subsidy payments. About 10 million people are enrolled in Obamacare through its marketplace, and most receive subsidies. Trump, who as a candidate last year promised to roll back the law formally called the Affordable Care Act, received applause for his latest action during an appearance on Friday before a group of conservative voters. “It’s step by step by step, and that was a very big step yesterday,” Trump said. “And one by one, it’s going to come down, and we’re going to have great healthcare in our country.” He said he was taking “a little different route than we had hoped” because of Congress’ inability to act. Republicans for seven years had vowed to get rid of Obamacare, but deep intra-party divisions have sunk their efforts to get legislation through the Senate. Trump on Friday called Obamacare “a broken mess” and urged Democrats to reach out to him to make a deal. “The Democrats ObamaCare is imploding,” he said in a Twitter post. “Massive subsidy payments to their pet insurance companies has stopped. Dems should call me to fix!” Since taking office in January, Trump has made the monthly subsidy payments, which Obamacare guaranteed to insurers to help reduce out-of-pocket medical expenses for low-income consumers, but that he had called a “bailout” for insurance companies. Trump had the power to stop the payments and previously had threatened to do so. The American Medical Association, the nation’s largest group of doctors, said it was “deeply discouraged” by the subsidies cut-off.