During an Iowa town hall last week, “Beto” O’Rourke, who had pledged to raise the level of national discourse, depicted President Donald Trump’s rhetoric as right out of Nazi Germany. Trump “describes immigrants as ‘rapists’ and ‘criminals'” and as “‘animals’ and ‘an infestation,'” said Beto. “Now, I might expect someone to describe another human being as ‘an infestation’ in the Third Reich. I would not expect it in the United States of America.” The crowd lustily cheered the analogy. By week’s end, Beto’s Third Reich comparison had been matched in nastiness by Bernie Sanders’ description of the president to the...