Trump calls for Congress to take action against 'lowlifes' who burn American flag

[Maeve]

32. And that was ruled against in 1990, US v. Eichman

In an opinion by Justice Brennan and decided along the same 5–4 lines as in Texas v. Johnson, the Court held that the federal government, like the states, cannot prosecute a person for desecration of a United States flag, because to do so would be inconsistent with the First Amendment. The Government conceded that desecration of the flag constitutes expressive conduct and enjoys the First Amendment's full protection. It is clear that the "Government's asserted interest" in protecting the "physical integrity" of a privately owned flag in order "to preserve the flag's status as a symbol of the Nation" and certain national ideals, is related to the suppression, and concerned with the content of free expression.

https://en.wikipedia.org/wiki/United_States_v._Eichman

It would take an amendment to get past the court and that isn't going to happen.
But yes, he doesn't know or care about actual law