California Governor Gavin Newsom took to the airwaves Tuesday night — with federal troops stationed in his state’s largest city and immigration agents rounding up residents — and warned Americans that democracy itself was under attack from President Donald Trump.

Trump’s administration promises to round up some 3,000 immigrants a day and deport 1 million a year, the political stakes are shifting in real time.

Gov. Gavin Newsom depicted the federal military intervention in Los Angeles as the onset of a much broader effort by Trump to overturn political and cultural norms at the heart of the nation’s democra...