I don't believe that "the use of DHS in Portland" violates any laws in itself. Could some actions the feds took violate the Constiution or DHS regulations? I don't know. I suspect DHS could justify its actions on the grounds that the "protesters" had been breaking the law for over a month in Portland and the feds were compelled to take action, but I didn't see everything that happened.
Another way to look at it: How is it legal or sane for the feds allow the rioters to burn down a federal building (even if people inside the building survive), if the fire spreads to other buildings?