As Democrats survey a troubled 2014 political landscape, it's easy to forget how optimistic they seemed less than a year ago. "I would expect that Nancy Pelosi is going to be speaker again pretty soon," President Obama told cheering House Democrats at a party retreat last February. In the rosy scenario that took hold in some Democratic circles, the party was positioned to recapture the House in 2014 and maintain control of the Senate, allowing Obama to defy the history of second-term presidential decline. Great successes and good years lay ahead. Had Democrats forgotten Obamacare, the law they passed in...