To maintain public order? Do the job of the city?

Is that specific posting the most valuable application of law enforcement resources to maintain public order? To stand there and keep a few dozen protestors from crossing into the ICE property? Seems pretty unlikely that that's the best use of a uniformed on-duty officer. Certainly not so obviously that you could say the Mayor is being derelict for not choosing to make that a priority, or the governor for not permanently posting state troopers.

So instead we have to have federal workers under constant threat of violence from the goons. Is that it?

It's a free country, so you don't ever get to be completely free of protests if people want to protest what you're doing.

Your governor wouldn't put up with this crap.

He didn't do much in 2020 during the Floyd protests, because there wasn't much he could do. That's why the legislature passed a whole bunch of changes to the criminal code, so that there actually were criminal violations that could be brought against people who engaged in this type of protest. I doubt there's anything similar on the books in Oregon. Plus, I doubt he'd take any action against a conservative-coded protest - like, say, an anti-abortion protest that got out of hand and started blocking traffic.