The campaign will grind along until a series of sharp moments. Maybe they will come in the debates. Things will move along, Mr. Obama in the lead. And then, just a few weeks out from the election, something will happen: America will look up and see the inevitability of Mr. Obama, that Mr. Obama has already been “elected,” in a way, and America will say, Hey, wait a second, are we sure we want that? And it will tighten indeed.