FiveThirtyEight noticed last week that, very quietly, Biden was recovering from the polling hit he took after the busing exchange with Kamala Harris at the last debate. Harris had zoomed up after that in some polls, even touching 20 percent in Quinnipiac’s June survey, but the trend didn’t continue. It was Biden who was once again on the rise while Harris dipped a bit.

Now here comes Quinnipiac’s July poll with even clearer evidence of the trend.

What happened?

Look back to the numbers from June. After a long slide in early July after the first debate, with Harris nearly passing him, Biden’s regained 12 points and now enjoys a bigger lead than he did before. And most of that 12-point surge has come at Harris’s expense. Check this out (“AA” is “African-American”):

Apparent Biden bounce in Q poll reflects recovery across the board, but most striking is re-consolidation of AA vote. Back at 53% (from 31%), with nobody else in double digits, down from 27% (Harris) and 16% (Bernie.) No apples to pre-debate apples, but seems ~full circle.

— Liam Donovan (@LPDonovan) July 29, 2019

A huge number of black voters migrated from Biden to Harris after the busing exchange … and now they appear to have come home to Joe. It’s not just happening in the Quinnipiac poll either. Over at RCP’s poll of polls, Biden has regained nearly all of the lead he enjoyed shortly before the first Democratic debate. In mid-June he stood at 32 percent with Bernie second at 15. Today Biden’s at 31.3 with Elizabeth Warren second at 14.8. Harris, the supposed breakout star of the last debate, is in fourth place at 11 percent — still several points higher than where she was before the busing attack on Biden but by no means threatening Uncle Joe for the lead.

Again, what happened?

Nate Silver speculated last week that the post-debate polls were affected by a burst of enthusiasm from Harris supporters. As that enthusiasm cooled a bit, the polling equilibrium was restored:

[O]ne contributing factor may be nonresponse bias — after a good debate for Harris and a poor one for Biden, for instance, Harris supporters may be more likely to respond to polls and Biden ones less so. I tend to think this phenomenon is a little overstated and that an easier answer is simply that a lot of voters don’t have deep convictions about the race until much later, and so bounce around among whichever candidates have gotten favorable press coverage recently.

The latter explanation about the lack of deep convictions makes more sense to me. Voters liked what they saw of Harris at the debate but they haven’t seen or heard much lately unless they’re so attuned to daily political news that they’re following the rollout of her Medicare for All plans, so they’re back in default mode. If I had to float a theory for why they’re reverting to Biden it’d be pure, clean, simple electability: Uncle Joe blows the field away when Dems are asked who stands the best chance of beating Trump, taking 51 percent of the vote when no one else does better than 10. Every day that Democratic voters are focused on the latest Trump outburst instead of the daily squabbling among Dem candidates is probably a good day for Biden inasmuch as Trump’s antics remind liberals that winning next fall is all that matters, which naturally leads them back to the safest, supposedly most electable choice.

The most frequently recurring narrative about the primary in political media this past week is Biden vowing to get his game face on for the upcoming debate. Literally every four hours or so, some media outlet regurgitates another “no more mister nice guy” piece about Uncle Joe. He’s been taking shots at Harris and Cory Booker too, partly to preview the battle to come on Wednesday night and partly to reassure nervous Biden fans who thought he looked a bit … frail at the first debate that he’s up to the challenge. I hope for his sake that that’s true. Because Philip Klein’s right that he’s staring down the barrel of a “Pawlenty moment” if he wimps out again when he’s face to face with Harris:

For those who need a reminder, Pawlenty was a governor of Minnesota who ran a failed bid for the 2012 Republican nomination. From the get-go, he was hindered by the perception that he was too boring and too much of a nice Midwesterner to survive the brutal world of presidential politics. Seeking to disabuse people of this perception, he used the run up to a summer 2011 debate as an opportunity to attack Romney’s Massachusetts healthcare law that provided the model for Obamacare. In interviews leading up to the debate, he deployed the phrase “Obamneycare” and talked about his sharp elbows from playing hockey. Everything was teed up for Pawlenty to swing at Romney’s biggest vulnerability. Yet when he was given the opportunity to challenge Romney on the debate stage, he totally bungled it. He didn’t merely wiff, he backed off his attack altogether. Pawlenty wouldn’t formally drop out of the race until August, but effectively, his chances were doomed once he blew his chance in the June debate.

Romney analogies usually aren’t good for Harris but she’ll take that one. Exit question: Will Biden wimp out? I think he’ll wimp out.