Yes, "The Congress shall have Power...To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions".

One of the ways Congress has done that was to pass the Insurrection Act, which was the legal basis for President Eisenhower to send 1,000 paratroopers from the 101st Airborne in to Little Rock, Arkansas in order to force racial integration of a high school.

The same act was used by JFK 3 times for similar purposes, 3 times by LBJ to suppress riots and civil unrest, by Reagan to suppress a prison riot, and by George H. W. Bush to deal with looting in the Virgin Islands after a hurricane, and to suppress riots in L.A. after the acquittal in the Rodney King beating trial.

There's also the 3rd Amendment quartering of troops restriction, so if you live in Portland, you won't have to let the troops stay at your house unless you want to, unless Trump declares war.

The feds own immigration policy and enforcement. For a city to declare itself a "sanctuary city" is, basically, a refusal of federal authority. Yeah, previous presidents didn't make an issue out of it. That doesn't make it anything different, though.

And the federal government does have the right to bring in federal troops to protect federal buildings and federal officials.

But of course it's not that simple. That presumes that Trump's actual reason is the stated one, which is not a reasonable assumption. It presumes that all the troops will do is protect federal property and workers, which is unknowable at present.

And it ignores the ruling that Trump bringing troops into LA was illegal. If that was a federal circuit ruling, well, Portland is in the same federal district, so it's current law there. (Does anyone know what the current situation is with that case? Does that ruling stand?)

Look, don't take any of this as an apology for Trump. But he does have the legitimate authority to enforce immigration law. If the troops wind up doing more than protecting the people who are doing that, then he doesn't have the legitimate authority to do that.