I agree with OP, any such action will bring up a dangerous precedent. I didn't like him even going there with his words, recalling the GOP using Biden's words as justification for not holding hearings on Obama's Supreme Court nomination.
Trump talks too much off the top of his head. If out of one side of his mouth Trump says the government shutdown can last for "years" until he gets money for the wall, I doubt he can convince the court when from the other side he states we have a national emergency. He does really well when he lets the professional speech writers do their job and uses the teleprompter.