President Donald Trump has deployed some 2000 National Guard troops to Los Angeles in response to protests against ICE deportation operations. As yet, the authority he has invoked for this domestic use of the military is very limited. See the detailed analyses of the relevant law by legal scholars Chris Mirasola and Steve Vladeck. That could change if Trump decides to invoke the Insurrection Act, which grants far broader authority to use the military for domestic law enforcement. Whether and to what extent that power is subject to significant limitations is controversial. For details, see this analysis by Elizabeth Goitein of the Brennan Center, a leading expert on this subject.
In the meantime, I worry that the current, relatively limited, deployment of troops, might lead to dangerous es