Like Gen. Francisco Franco in 1970s episodes of Saturday Night Live, Mitt Romney's momentum is still dead. The eight tracking polls I've been reporting on since they started reflecting post-debate polling show a net drift, since Monday's final pre-debate polling, of 0.9 points toward Obama (compared with 1.0 yesterday, 0.6 the day before, and 0.9 the day before that).



But this stasis could get disrupted any day now. About 5 percent of voters are still telling pollsters they're undecided. And traditionally,* late-deciding voters -- which this 5 percent certainly qualifies as -- wind up mainly voting against the incumbent.

The most interesting analysis of this phenomenon I've seen lately -- and the most alarming for Obama supporters -- comes from Bob Krumm (no, not Bob Shrum, and for that matter not Robert Crumb). Take a look at this collation he's done of this year's polling results and the polling results from 2004, the last time we had an election featuring an incumbent. The dashed purple line and the solid blue line represent the incumbents in, respectively, 2004 and 2012, and the other two lines represent the challengers.

Note the relative fortunes of the challenger and the incumbent in polling done during the final week of 2004. That looks like more than 1 point of net gain for the challenger. That's the kind of thing that could erode the peace of mind of Obama supporters. Here's another such thing: New York Times polling guru Nate Silver -- whose forecast currently gives Obama a 70-something percent chance of winning and is a daily source of reassurance for many Democrats -- has a model that fails to take adequate account of the dynamic on display in 2004. At least, that's what Krumm says. He says Silver's model is too heavily informed by the 2008 election, which was unusual in featuring neither an incumbent nor a presidential candidate who was the sitting vice president. [But see update below for a link to Silver's questioning the conventional wisdom that undecideds regularly break toward the challenger.]