Since the Affordable Care Act was instituted, also known as Obamacare, insurance companies have been prohibited from refusing coverage on the basis of pre-existing conditions. Trump has railed against Obamacare since his campaign, and has tried to weaken its provisions since taking office. He repeatedly attacked John McCain for being the deciding vote in preventing the repeal of the ACA. Despite this, Trump tried to claim via tweet that he was the person who saved the pre-existing conditions provision, and promised to protect it.

Trump’s confusion regarding healthcare is not a new phenomenon, as he had previously remarked how “nobody knew that healthcare could be so complicated.”

Politico – Why McCain screwed the GOP on Obamacare repeal — again
The New York Times – To the Contrary, Trump Has Tried to Weaken Protections for Pre-existing Conditions
US News & World Report – AP FACT CHECK: No, Trump Didn’t Save Preexisting Conditions
Newsweek – TRUMP CLAIMS HE ‘SAVED’ PRE-EXISTING HEALTH CARE CONDITIONS, BUT HIS ADMINISTRATION WANTS TO KILL THEM