apparently doesn't understand that stealth fighters are not invisible. He has said it several times, in public, including today, in a speech to veterans. He also didn't know that Frederick Douglass was dead (or who Frederich Douglass is). As candidate for office, both in interview comments and in a debate with Hillary Clinton, he said things that showed he didn't understand what the Affordable Care Act is. He claimed that Obama was born in Kenya. He refused to accept the exoneration of the Central Park Five. He uses language about the press and immigrants that is full of toxic lies. I could go on.
One of his biggest supporters, Alex Jones, who is being sued for defamation by the parents of children killed in the Sandy Hook massacre, said on Facebook live today, on his channel that has over 1.5 million subscribers, that Robert Mueller rapes children. He did not mean it metaphorically. Jones's extreme views have entered into the thinking of the president's supporters. People will take Jones's lies as true and use them to undermine, if not kill, Robert Mueller and his staff.
We have legal limits on free speech for a reason.