The National Guard has always been deployed in case of emergencies nationwide and US Presidents have always called on the National Guard (or State militias, before that was formalized) to assist in federal matters.

Washington himself took command of state militia units during the Whiskey Rebellion.
Lincoln called on state militias right at the beginning of the Civil War to help fight the Secessionists.
Eisenhower famously federalized the Arkansas National Guard in order to sucessfully integrate public schools against the wishes of Governor Faubus.
Johnson took control of the Alabama National Guard to have them protect the civil rights activists during the famous Selma March.
Heck, Biden had 21 *thousand* guardsmen in DC for a few weeks before and after his inauguration to support law enforcement (all the while barricading the White House to make sure no one could access it).

What Trump is doing is not fundamentally different from what any other President has done in similar circumstances - and in fact from a strictly constitutional point of view, it is a lot less worrying than a President taking control of the State National Guard to go against the State Governor, something that Eisenhower did.


Ultimately though, no matter how much you lot may cry and complain about it, what matters is that it is working.
Criminals in DC are getting arrested by the dozen and the streets are starting to get back to a "safe to walk in the neighbourhood" level; which is not something that should be so shocking in the nation's capital.

And that's why outside of the "experts" echo chamber and crying circles, the people who couldn't even walk on the streets are overwhelmingly supporting this move.