(I suppose it's really more of a reverse valley, which could make it a peak; or you could call it a sweet spot. But given that it's the RomneyTron 9000 we're talking about here, it's hard not to think of "Uncanny Valley", heh.)
So here's my thesis. Romney had all kinds of trouble throughout 2011 trying to get atop the polls. One GOP insurgent after another surged ahead of him, and each time they fell back into the pack, another took their place. Then in late December and early January, he actually managed to get up top himself, and--other than a hiccup in South Carolina--seemed to have consolidated his position after the first four contests once he took Florida down. But as we know, since then he has once again struggled mightily. What happened?
My hunch is based on the widely held idea that most Republicans don't really like or trust Romney, so his raison d'etre as a candidate is as the "electable" one, the guy who can beat Obama. Back in summer and fall 2011 that was a weak argument because Republicans were confident (cocky, even) that Obama was toast. Any nominee could beat Obama, they reasoned; so why not nominate a true believer? (Michele Bachmann, you may recall, made this exact pitch explicitly.)
Then, on December 2, out came that sweet, sweet jobs report. Just as we Democrats cheered the good news, that same report made GOP blood run cold. "Uh oh", they thought, "we could lose this thing". All of a sudden going for a pragmatic nominee that could eke out a victory on a tough playing field began to look more attractive, and if you look at the RCP graph, that was the precise moment Romney started climbing back up in the polls.
The last part of it is what made me think of it in similar terms to the "uncanny valley" concept, albeit in reverse. This new dynamic favoured Romney, as long as it looked like Obama was neither easy to beat nor impossible to beat. But there has more recently been a steady drumbeat in the media, from TV pundits, and just in the zeitgeist, that Obama is increasingly looking like a shoo-in to win in the fall. (I'm aware of the danger of our being overconfident; I'm just describing the CW that is likely weighing on GOP voters' minds.) Once that idea sinks in, I think a lot of GOP voters return to a kind of Bizarro-world version of the mentality they had last fall: "Screw it, if we can't beat Obama anyway, we may as well nominate someone we like, who really represents us, instead of some prissy Northeastern milquetoast who only pretends to be conservative to get our votes."
Which of course is fine by me. Who knows what "October surprise" could come our way; and should something happen, I'll feel much more comfortable if the GOP nominee is someone that moderates and especially women find absolutely unacceptable.