Trump's threat to invoke Insurrection Act escalates showdown with Democratic cities

The law, which gives the president authority to deploy the military to quell unrest in an emergency, has typically been used only in extreme cases, and almost always at the invitation of state governors. Since his second term as president began in January, he has shown little hesitation in seeking to wield governmental authority against his political opponents, as he pushes to expand the powers of the presidency in ways that have tested the limits of the law. The act, a version of which was first enacted in 1792, has been used by past presidents to deploy troops within the U.S. in response to crises such as rise of the Ku Klux Klan after the American Civil War.