The Trump administration claims that the border patrol is in Portland on just such a mission — protecting federal property, including a courthouse. But that pretext cannot be squared with federal officers dispersing protesters and arresting people far from federal buildings.
Nor is the claim of protecting federal property consistent with Trump’s much broader assertion that he is using federal officers to combat anarchists and restore order. It is also highly questionable that the federal border patrol may be involved in actions that have nothing whatsoever to do with border enforcement, especially in places, like Chicago, many hundreds of miles from any border.
As to what the president can’t do: Federal law enforcement personnel cannot be used to enforce state and local laws. It’s basic to the Constitution — state and local governments have the police power; federal officers are limited to enforcing federal law. But Trump clearly says he is sending officers to cities with “liberal Democrats” as mayors as a way to stop protests and “restore order.” Absent invoking the Insurrection Act, he simply does not have the power. Ironically, it is conservatives — Republicans — who have usually championed federalism and respect for the authority of state and local governments, but not Republican Donald Trump.
Another can’t: The president cannot authorize violations of the First and Fourth Amendments.