In CNN’s last poll, taken soon after the Democratic convention, O led by six among likely voters. That lead’s now cut in half, to within the margin of error, despite weeks of media doomsaying about Romney’s campaign. In fact, the last four national polls all have the race within two or three points with a bounce opportunity for Romney looming 48 hours from now. I think the first debate will essentially be an audition for him: Obama’s the ultimate known quantity but, for millions of low-information voters, this’ll be the first time they see Romney in action. If he’s as composed and articulate as he was in the GOP primary debates, he’s bound to see some positive movement among undecideds regardless of what Obama does.

Even more encouraging here: As our Greenroomer Karl pointed out on Twitter, Obama’s lead among registered voters (50/46) is almost identical to his lead among likely voters (50/47), which means there isn’t much difference in the partisan split between the two samples. That’s unusual; typically a sample of likelies is a few points more Republican than a sample of registereds. So, if anything, CNN might be underestimating just how well Romney’s doing right now. Also, note that not only does Romney lead by eight among CNN’s (tiny) sample of independents, but his support from Republicans is even more solid than Obama’s support from the Democrats:

There must be a decent Democratic lean in the overall sample of likely voters (which CNN doesn’t publish) to produce that result. (Update: Yep. See below.) The money question, then: What’s causing the race to tighten? Is it a natural phenomenon as more casual voters start to pay attention? Is it, as CNN’s pollster suggests, a case of Obama’s post-convention bounce disappearing? Or is it public disgust with the Foreign Policy President’s performance on Libya? Here are the numbers on FP, where O’s lead is down five points from last month:

Suggestive, but not proof that that’s what’s driving this. Let’s see if we can find decline in any of his other numbers. How about … this?

Romney had a big lead initially, then it shrank after the conventions, and now it’s ballooning again. More:

Another huge fade as the convention recedes. I think CNN’s right: O got a bounce, which was possibly extended a bit past its normal shelf life by the “47 percent” kerfuffle, and now Americans are remembering that they don’t much like him without Bill Clinton on TV to convince them that they do. In fact, Obama’s favorable numbers are now nearly the same as Romney’s, 52/48 for The One and 49/50 for Mitt with possible movement to come on that Wednesday night. Most damning of all, check out his job approval — and note how long it’s been since he was this close to the water line:

That makes me think there’s more to this than just a fading bounce. Exit question: What’s happening here? Libya backlash, normal October tightening, or an early sign that undecideds are finally ready to pass on another four years of Hopenchange dreck?

Update: An oversight on my part: CNN did publish the partisan split this time, on page 15 — and it’s D+8 (37D/29R/34I). The turnout on election day 2008 was only D+7, and nobody but nobody thinks O will approach that this year. So this poll looks even better for Romney than I thought.