Republicans should be able to retake the Senate in November, but they may blow their chance by nominating candidates whom too many voters find offensive. A leading example is Missouri Republican Senate candidate Eric Greitens, who is running a TV ad that shows remarkably bad judgment, even for him.

The online ad has Mr. Greitens toting a shotgun and declaring that he’s hunting for “RINO,” short for a Republican In Name Only, who the ad says “feeds on corruption and is marked by the stripes of cowardice.” Armed men in military gear break into a home in the ad, followed by Mr. Greitens, who exhorts: “Join the MAGA crew. Get a RINO hunting permit. There’s no bagging limit, no tagging limit, and it doesn’t expire until we save our country.”