The biggest lie that President Trump and other Republican leaders have been repeating about the Affordable Care Act for years is that it is collapsing, imploding or exploding. The truth is that the law is actually working reasonably well, and even the part that has shown the most weakness — the health insurance marketplaces — has been stabilizing.

Insurers that sell policies to individuals and families are doing better financially than in the first two years of the A.C.A. They are also doing better than they were before the federal and state governments opened the marketplaces in 2014, according to a Kaiser Family Foundation report published on Monday. The data showing improvement confirms earlier reports by Standard & Poor’s, the Congressional Budget Office and research groups that were based on 2016 numbers. While there are still problems in marketplaces in some states, the A.C.A., or Obamacare, is hardly coming undone.

Yet Republicans in Congress and the Trump administration continue to peddle horror stories about the A.C.A. as they try to gather the votes for repeal of major provisions of the law. To that end, the Senate majority leader, Mitch McConnell, says he will present a new version of his health care bill on Thursday. His earlier proposal would take health insurance away from 22 million people and raise premiums for millions of others, according to the C.B.O. There is no indication that the changes he has in mind will meaningfully improve that dreadful legislation.

Many Americans who do not get health insurance through employers have been frustrated with the marketplaces. The launch of HealthCare.gov by the Obama administration was disastrous. And the insurance policies have high deductibles and premiums that are unaffordable to many people, because the law did not provide enough subsidies to middle-income families. Insurers did a poor job designing their policies and suffered big losses initially, forcing them to raise premiums even more. Republicans also weakened the markets by repealing provisions meant to stabilize them and by filing a lawsuit to reduce federal subsidies. Despite these challenges, more than 10 million people have bought policies on the marketplaces. Most have been protected from big premium increases through subsidies.