Fed up with resistance from the legislature, the South Korean president tried to declare martial law in the name of “democracy.” The public resisted, the military had little appetite for the task, and the constitutional guardrails held. Could you imagine Trump doing the same thing if the GOP does poorly in the midterms?
Of course you can! And, thanks to the Supreme Court, the base, and a core of craven supporters in Congress, he can’t be prosecuted or removed from office through the impeachment process. He will have appointed the new heads of the military, too.
It would be a mistake to assume he won’t try it just because there is no American precedent for it. The consequences for trying and failing will be minimal, and the benefits to him of succeeding would be quite large.