While Trump has thus far failed to fulfill his campaign promise of repealing and replacing former President Barack Obama’s signature health care plan, he appeared to get a second wind last week. The Justice Department sided with a federal judge in Texas, who ruled in December that the law’s individual mandate was unconstitutional and that the rest of the law was therefore invalid—despite the Supreme Court previously upholding the law in 2012.

The Texas ruling calls into question one of the key components of the ACA: protection for those with pre-existing conditions. But Acting White House Chief of Staff Mick Mulvaney sought to assuage the concerns of those with such pre-existing conditions over the weekend, while speaking on ABC’s “This Week.”

Mulvaney told ABC News White House Correspondent Jonathan Karl that he could guarantee that those with pre-existing conditions would not lose their coverage, claiming that “every single plan that this White House has ever put forward since Donald Trump was elected, covered pre-existing conditions.” But Mulvaney failed to provide additional details and did not address how the millions of others who get their coverage through healthcare.gov and state exchanges would continue to do so.

So what does happen if the Affordable Care Act is struck down?

The short answer is we don’t really know yet, because we haven’t seen an alternative plan. Trump said last week that if the law is struck down “we will have a plan that is far better than Obamacare,” but didn’t elaborate on such a plan.

The Urban Institute’s Health Policy Center estimated in a study released last month that 19.9 million Americans could lose their coverage, increasing the number of uninsured by 65%. And it’s not just those who get their insurance from the exchanges or through ACA’s Medicaid expansion who could be affected.

The Affordable Care Act also includes provisions that decrease costs of Medicare coverage and prescription drugs for senior citizens, another that allows children to stay on their parents’ health insurance plans until they turn 26 years old, and lets many Americans get birth control, mammograms, and cholesterol tests for free. Even the Trump administration’s policy priority to lower prescription drug prices relies on ACA.

President Trump had reportedly asked three Republican senators to take on the challenge of developing a new Republican healthcare bill, but these senators, John Barrasso, Bill Cassidy, and Rick Scott don’t appear to know whether an alternative plan will be forthcoming. The Washington Post reported over the weekend that Republicans “have no intention of heeding President Trump’s urgent demands for a new health-care plan to replace the Affordable Care Act,” adding that “not only is there no such health-care overhaul in the works on Capitol Hill—there are no plans to make such a plan.”

The lukewarm response from members of the Republican Party—and the sharp criticism from Democrats—appears to have delayed Trump’s plans, for now. Late Monday, Trump indicated that Republicans in Congress would wait until after the 2020 election to vote on an ACA replacement.

In a series of tweets, Trump wrote that “everybody agrees that ObamaCare doesn’t work” and that Republicans are therefore “developing a really great HealthCare Plan with far lower premiums (cost) & deductibles than ObamaCare. In other words it will be far less expensive & much more usable than ObamaCare.”

He went on to add, “Vote will be taken right after the Election when Republicans hold the Senate & win back the House. It will be truly great HealthCare that will work for America. Also, Republicans will always support Pre-Existing Conditions. The Republican Party will be known as the Party of Great HealtCare [sic]. Meantime, the USA is doing better than ever & is respected again!”