What explains Mr. Obama’s consistent snubbing of those who made him what he is? Does he fear that his enemies would use any support for progressive people or ideas as an excuse to denounce him as a left-wing extremist? Well, as you may have noticed, they don’t need such excuses: He’s been portrayed as a socialist because he enacted Mitt Romney’s health-care plan, as a virulent foe of business because he’s been known to mention that corporations sometimes behave badly.

The point is that Mr. Obama’s attempts to avoid confrontation have been counterproductive. His opponents remain filled with a passionate intensity, while his supporters, having received no respect, lack all conviction. And in a midterm election, where turnout is crucial, the “enthusiasm gap” between Republicans and Democrats could spell catastrophe for the Obama agenda…

Just to be clear, progressives would be foolish to sit out this election: Mr. Obama may not be the politician of their dreams, but his enemies are definitely the stuff of their nightmares. But Mr. Obama has a responsibility, too. He can’t expect strong support from people his administration keeps ignoring and insulting.