No, it is not. It is expressly permitted for the president to take control of the National Guard in very specific circumstances "the President is unable with the regular forces to execute the laws of the United States" uscode.house.gov/view.xhtml?r...
In the event of an insurrection, where the president is unable to defend himself with existing law enforcement. Is that what’s happening?
The problem with what Trump did was he did not go through the governor to activate the National Guard like Title 10 requires, so he is violating the law.