As he headed to Huntsville, Ala., in a last-ditch effort to lift the floundering campaign of Sen. Luther Strange, President Trump was fuming — feeling dragged along by GOP senators who had pleaded with him to go and increasingly unenthusiastic about Strange, whom he described to aides as loyal but “low energy.” His agitation only worsened on the flight back last Friday. Trump bemoaned the headlines he expected to see once Strange was defeated — that he had stumbled and lost his grip on “my people,” as he calls his core voters. He also lamented the rally crowd’s tepid response...