President Trump has long mused about using troops to crush violent protests or riots in blue-state cities. He is now moving to do so in Los Angeles.Setting up a rare use of military force on domestic soil, President Trump ordered the Pentagon on Saturday night to send at least 2,000 National Guard troops to respond to protests in Los Angeles set off by his immigration crackdown.Mr. Trump has long mused about using military force on domestic soil to crush violent protests or riots, fight crime and hunt for undocumented migrants — a move that his aides talked him out of...