I have a lot of Democratic friends who are extremely disappointed with their party leaders. They tell me that the Democratic Party is currently rudderless, weak, passive, lacking a compelling message. I try to be polite, but I want to tell them: “The problem is not the party leaders. The problem is you. You don’t understand how big a shift we’re in the middle of. You think the Democrats can solve their problems with a new message and a new leader. But the Democrats’ challenge is that they have to adapt to a new historical era. That’s not something done...