https://edition.cnn.com/2020/06/01/politics/donald-trump-national-address-race/index.html
The President made a brief appearance outside St John’s Episcopal Church near the White House last night. He was clutching a bible and surrounded by a heavy security presence who tear-gassed and bludgeoned peaceful protesters away from the vicinity of the church to enable the president and the WH press corps to make the short journey to the church which has traditionally been used by many presidents in the past.
"If a city or state refuses to take the actions necessary to defend the life and property of their residents, then I will deploy the United States military and quickly solve the problem for them," Trump announced.
Bishop Mariann Edgar Budde who oversees the St John’s Episcopal Church later said she was outraged that a church within her diocese had been used without permission as a visual backdrop for delivering a political message that was antithetical to the teaching of Jesus.
Trump appears to be threatening to invoke a rarely used piece of federal legislation known as the Insurrection Act 1807. The problem is that he has no authority to do so nationwide on any unilateral basis.
https://en.wikipedia.org/wiki/Insurrection_Act
The act in question specifically prevents a president from despatching active US military personnel on law enforcement missions unless state governors have petitioned him to do so, and only after exhausting all other resources.
President George W. Bush attempted to invoke the Insurrection Act in Louisiana during the 2006 Hurricane Katrina disaster, in spite of the governor refusing to countenance such a move because it was unconstitutional. The Bush administration then tried to alter the law by stealth, but all 50 state governors issued a joint statement against the legal changes, which were promptly repealed in 2008.