9 p.m. ET across the dial. It’s true that VP debates usually don’t matter, and Gallup has the data to prove it. It’s also true that the shellacking Romney gave to the Empty Chair in Denver has created an unusual and unpredictable late swing in momentum. What we’re looking at tonight, then, isn’t so much a potential gamechanger as an opportunity to preserve a game that’s already changed. If Ryan makes a good impression, it’ll cement the impression Romney made at the last debate and give undecideds more confidence in rolling the dice on the new guys. That makes Biden’s task simple: Ensure that Ryan doesn’t make a good impression by calling him a liar, a woman-hater, blah blah. Dave Weigel went back through the Biden debate archive and found that he’s perfectly comfortable in that role:

The Clatworthy debates give us a better idea of Biden’s style than the Palin debate of 2008. That match-up was sui generis. Biden’s job then: Just don’t do anything that would make a swing voter root for the put-upon Hockey Mom. But Biden’s job, in his Senate races, was to humiliate Republicans by pointing out how cruel their policies were, and how little they knew. Abortion and women’s safety issues, which he could never deploy against Palin, are the tools he knows best. When Biden meets Ryan tonight, it would be out of character if he didn’t try to mire him in a discussion of pro-life bills and “legitimate rape.” Plenty of pols use soft language when they have to discuss those issues. Biden doesn’t.

Really, whenever an issue can be mined for pathos, Biden thrives. In the second Clatworthy debate, after the Republican failed to trap the senator into a joint PAC money-pledge press conference (“See if anyone shows up and pays attention to you,” said Biden), moderators switched the discussion to entitlements. It was 1996, and the fiscal problem du jour was whether to balance the budget by 1999 or by 2002. Clatworthy suggested that a privatized Social Security system and privatized Veterans Affairs administration would be more efficient. Biden reacted like he’d just heard a Tourettes patient question the death toll of the Holocaust.

A few days ago I predicted plenty of table-pounding atmospherics from Greasy Joe in the name of re-energizing deflated liberals and winning back wavering middle-class indies. With Obama advisors now telling Politico to expect a “very aggressive” debate, I’ll stand by that. He’s not going to win this on substance, but if he gets outrageously outraged enough, the media will award him the decision on “style” for having effectively channeled their own anger at the prospect of a GOP win. (Besides, it’s the first step in the inevitable “Obama comeback” narrative.) Hope Ryan’s ready to repel a sustained effort to keep him on the defensive, especially since, with Biden’s favorables already underwater, he doesn’t have to worry about coming off as a nice guy. Read Ace for more on why it’s foolish to underestimate him: The moderator’s under pressure not to anger the left the way Jim Lehrer did, all issues — including easy demagogue-able “war on women” trivia — are on the table, and Biden’s proved plenty of times that he’s good enough behind a mic to impress low-information voters. The left needs someone tonight who can grandstand effectively, not out-brainiac Ryan on federal budget minutiae. A guy who got elected to the Senate six times and then to the vice-presidency can grandstand effectively.

Robert Costa has a nice piece on Ryan’s exhaustive debate prep so read that while you’re waiting for the show to start. (Note the bit about Ted Olson mimicking Biden down to his hand gestures.) One obvious X factor: How much time will moderator Martha Raddatz spend on the White House’s Benghazi clusterfark? A Romney advisor told Byron York that Ryan’s prepared to hammer Obama’s “unraveling” foreign policy, but that he probably won’t get into the weeds on Libya and the subsequent cover up. That might be for the best: When it comes to terrible foreign-policy decisions endorsed by his opponent tonight, there’s an awful lot of other ground to cover.

Here’s the handy dandy Hot Air/Townhall widget for debate live-tweeting. If you’re looking for drinking-game rules, Reason has got you covered. Exit quotation: “Joe just needs to be Joe.”

Tweets from @erikajohnsen/townhall-hotair