A friend of mine who lives in Texas is representative of voters who will decide the 2020 presidential race. He supports many of President Trump’s policies but winces at his behavior, words and unpresidential tone.

You’d think Democratic candidates would be trying to gain his vote or at least multiply his doubts about Mr. Trump. Instead, they lose all sense of proportion. Many blame the mass shooting in El Paso on the president. They say he’s a racist who motivates other racists to go on shooting sprees. To my friend, these...