According to Trump, liberal cities are "out of control" and their leaders are "afraid" of the "anarchists" ("these are not protesters", "these are people who hate our country") and that's why they don't want the federal government to "help".
No, I don't think that's it.
What is happening in Portland is appalling, and Trump just threatened to send his goons into other cities over the objections of local governments. The people he's sending in are wearing generic fatigues (making them indistinguishable from mobs of neo-Nazis and other civilian thugs), driving unmarked rental cars, and snatching people off the streets. There is no due process, no accountability, and plenty of reason for those being targeted to fear the snatchers. You just can't tell. Even if you could tell, what they're doing is so far outside the bounds of the law that it's hard to believe it's happening and hard to believe there won't be further abuses even if you comply with these "arrests".
And yet, it is happening. Just when you thought the shenanigans coming from Washington couldn't get any worse.