He actually asked this at yesterday's WH press conference:
"Jon Karl just asked McEnany where in the Constitution does the Trump have the right to send law enforcement into these cities against the will of the local officials. It would start with Article II.
Federal enforcement is not "by invitation only." The use of federal agents to protect federal property or enforce federal law does not depend on local permission. There may be legitimate questions on how that authority is used but not the right to use the authority."
https://jonathanturley.org/2020/07/21/can-president-trump-really-send-in-the-troops-to-chicago-and-other-cities/