We were reminded yet again this past weekend that Joe Biden might be in deep electoral trouble. Once again, hands were wrung. This latest bout of alarm was occasioned by a New York Times/Siena College poll showing that only 23 percent of Democratic-primary voters said they are enthusiastic about President Biden’s candidacy. Forty-five percent said Biden should not be the party’s nominee. And Donald Trump led by five points in a head-to-head matchup. Yes, voters overwhelmingly believe that Biden is too old to be running for another term. He looks old, walks old, and seems not as sharp as he once was. This is not a new story. The premise has been challenged vigorously by the White House—to no avail. But there might be more to voters’ acrimony toward Biden than just his age. In speaking with Democrats about the president’s reelection chances, I often pick up a sharp tone that goes beyond resignation. It sounds more like rage. Senior citizens are not unpopular, per se. Biden himself was relatively well liked into his 70s, …