By Tami Luhby, CNN

President Donald Trump has long sought, unsuccessfully, to kill the Affordable Care Act, which established an unprecedented level of protection for those with pre-existing conditions.

But on Monday, he claimed credit for being "the person who saved Pre-Existing Conditions in your Healthcare" in a tweet blasting an ad by former New York City Mayor and 2020 Democratic candidate Michael Bloomberg that attacks the President's record on health care.

The ad is one of three Bloomberg health care spots running in at least 26 states, according to the campaign.

Facts First: Trump's claim about protecting those with pre-existing conditions is false. Though Trump says he would do this, his administration has consistently taken steps to undermine the Affordable Care Act -- including joining a lawsuit aimed at striking down the law -- without presenting alternative plans that would offer similar benefits.

The Affordable Care Act barred insurers in the individual market from denying people policies or charging them higher premiums because of their health histories. Also, carriers had to provide comprehensive coverage -- offering 10 essential health benefits, including maternity, mental health and prescription drugs.

About 54 million people had a pre-existing condition in 2018 that would have led them to be denied coverage prior to Obamacare, according to the Kaiser Family Foundation, a non-partisan research group. As many as 135 million people -- or about half of non-elderly Americans -- could have faced discrimination in the individual market before the law was passed, according to the Center for American Progress, a left-leaning advocacy organization, which based its figure on a Department of Health & Human Services report released in the waning days of the Obama administration.

Trump has worked to undermine the Affordable Care Act from his first day in office, when he issued an executive order directing agencies to interpret its regulations as loosely as possible. He championed congressional Republicans' bills that year that would have weakened the law's protections -- which are among its most popular provisions and helped Democrats retake the House of Representatives in 2018.

And his Justice Department is siding with a coalition of Republican states that are fighting in federal court to invalidate the Affordable Care Act. An appellate panel last month upheld a lower court ruling that found Obamacare's individual mandate unconstitutional but sent the case back to the lower court to decide whether the entire law must fall.

Bloomberg, who called Trump's prior assertions to protect those with pre-existing conditions a "broken promise" in the ad, responded on Twitter that the President should ask the Justice Department to drop the lawsuit.

The law remains in effect while the case works its way through the court system. The administration last week told the Supreme Court in a filing that there's no rush for them to review the appellate court's ruling -- which Obamacare's defenders, a coalition of Democratic states and the House of Representatives, are pushing justices to do. They argue that the lower court opinion poses a "severe, immediate and ongoing threat" to the nation's health care markets.

The President has said repeatedly that he would roll out a new health care plan that would protect those with pre-existing conditions, but he has yet to do so. Last April, he backed away from pushing for a vote on a replacement plan until after the 2020 election.

Meanwhile, he issued another executive order in late 2017 that would make it easier for Americans to buy alternatives to the Affordable Care Act that are cheaper, but offer fewer protections, such as short-term health plans. The law's defenders, however, fear that such plans could siphon off younger and healthier people, which could cause premiums to rise for those left buying policies in the Obamacare exchanges.

His administration is also allowing states to make major changes to their Obamacare markets, which could also leave low-income, older or sicker residents with few choices and higher costs. Few states have taken the federal government up on this offer so far.

The White House defended Trump's actions, saying in a statement: "President Trump has repeatedly stated his commitment to protect individuals with pre-existing conditions and his track record shows that he has consistently done what is necessary to improve care for the vulnerable by opening affordable options for those who were priced out of the market by Obamacare, combating the opioid epidemic, protecting and improving Medicare, enacting Right-to-Try, advancing kidney health, approving more generic drugs than ever before, committing to end HIV/AIDs within 10 years, and much more. While the media refuses to cover the ineffective provisions of Obamacare that have made health care too expensive for too many, the radical left is doing Americans with pre-existing conditions a disservice by making them a political pawn in their agenda to expand the scope of government."