Messrs. Obama and Trump represented a mood. They didn’t ask for or elicit rigorous judgment, they excited voters. Mr. Trump’s election was driven by a feeling of indignation and pushback: You elites treat me like a nobody in my own country, I’m about to show you who’s boss. His supporters didn’t consider it disqualifying that he’d never held office. They saw it as proof he wasn’t in the club and could turn things around. His ignorance was taken as authenticity. In this he was like Sarah Palin, another magic pony.

After two wars and an economic crisis, Mr. Obama gleamed with hope and differentness. This shining 47-year-old intellectual—surely he’ll turn things around. He’d been an obscure and indifferent state legislator who was only two years in the U.S. Senate when the move to make him president began. It was all—a feeling. He was The One. Mr. O’Rourke, who’s shooting up in the polls as a possible Democratic contender, is sunny, friendly, even-keeled. He reminds some Democrats of Bobby Kennedy—soulful, able to see and summon the things you like best in yourself. He even looks like a son of Bobby Kennedy. He is 46, has served only six years in the House, and before that was on the City Council of El Paso, Texas.

Our public political culture has given in too much to emotionalism.