With Los Angeles convulsed by confrontation between pro-migrant protesters and military units dispatched by Donald Trump, no figure apart from the president has loomed larger than Stephen Miller. As the man in the Oval Office, it is Trump who has absorbed the accusations of authoritarianism for usurping the powers of California’s government after deploying 4,000 national guard troops and 700 active marines on to the streets of a city that is home to more undocumented immigrants than any other in the US. Behind the scenes, however, this has been the apogee of Miller’s power – and an episode that illuminated...