“However the 9th Circuit ultimately comes down on that question, any decision addressing the legal merits of Newsom’s argument will amount to a rejection of the Trump administration’s alarming position that the president has the authority to deploy National Guard troops at will, even without pretending to meet statutory requirements or citing any facts to support his decision. That argument would transform the National Guard, today’s version of the state militia, into a federal force that the president can use at his discretion, without regard to constraints imposed by Congress or the 10th Amendment.”