The media have focused on the Nancy Pelosi-Donald Trump feud on display at Tuesday’s State of the Union address. But for our money the most notable part of the evening, and perhaps the most politically consequential, was President Trump’s pitch for African-American support.

Progressives cast all Republican politicians as avatars of racial resentment, and Mr. Trump has sometimes made himself an easy target. He once trafficked in birther conspiracies about Barack Obama, and he botched the response to the Charlottesville white-supremacist...