The headlines documenting President Donald Trump’s plan to send federal troops to San Francisco followed a familiar arc. “Trump claims ‘unquestioned power’ in vow to send troops to San Francisco,” The Guardian reported on October 20. The next day, the San Francisco Chronicle blared: “S.F. threatens to sue if Trump brings in National Guard.” Then, on October 23, “Trump reverses his decision to send troops to San Francisco,” as ABC News put it, after Trump posted that conversations with the city’s mayor and tech moguls had swayed him. It was another example of how Trump’s shifting policy positions, racially inflammatory...