Robert Paquin III is a Maine resident and former executive director of the Rhode Island Republican Party. For years, many Democrats have described Donald Trump as a “never again” moment in American politics. They were right. No party should excuse a man’s conduct or character simply because his message gives angry voters a voice. But that principle only means something if it still applies when the warning sign appears in your own colors. I say that as someone who knows the Republican side of this bargain. I served as executive director of the Rhode Island Republican Party during a cycle...