There is a president named Bush with high public-approval ratings. There is an economy that is sputtering, even on the best of days. There is a military triumph in Iraq that suddenly doesn’t look all that triumphal. There is, according to a theory the Democrats have developed in the tiny spot where history and hope collide, reason to believe that all those factors will combine to invite them back into the White House.

It happened once, and in theory it can happen again. History doesn’t repeat itself, but it sometimes can seem repetitive. And history does present an intriguing juxtaposition of facts: Only one other presidential son has been elected to the White House. He did so without winning the popular vote. Four years later, John Quincy Adams was not re-elected.