Nominees Bill Clinton and Al Gore wave to a crowd on the floor of the Democratic National Convention at Madison Square Garden in 1992. (Photo by Steve Liss/Contributor via Getty Images)A recent Nate Silver post posed “12 questions for the center-left.”It’s one of the best pieces I’ve read on the factional politics of the Democratic Party, in part because it raises great questions, but in large part because unlike most commentary, it actually ack…