Political experts are criticizing Donald Trump after the ex-president doubled down on a proposal he made last week, saying that people who burn the American flag should be jailed. MSNBC’s Jordan Rubin noted in an article last week: The legal problem with that proposal is that it violates the First Amendment. The Supreme Court addressed the issue in the 1989 case Texas v. Johnson, when conservative icon Antonin Scalia joined the high court majority in deciding that a conviction for burning the flag was unconstitutional. Trump repeated the proposal during his speech at the National Guard convent…