Yes, I'm aware of the threat.
We'll see if he actually does it. My instinct is the same as yours, but that's speculation.
To me, this is all the more reason to chill out on crying fascism over the detention of Khalil. Beryl Howell in DC today -- not the judge in his case -- ruled for Perkins Coie and said the idea of targeting people based on viewpoints "sends shivers down her spine." That's going to be the attitude of most federal judges, including the majority of Trump judges.
Take to the streets when the court orders are ignored. Until then, work within the system. Put up a fight in that way. Ask "what would Mitch McConnell do" and then do that.