Will the VP debate become an ugly partisan fight?

This post originally appeared on Slate.

Joe Biden has said that the hardest thing about becoming a vice presidential candidate was that he had to learn how to speak for someone else. It's been pretty hard on Barack Obama, too--because sometimes it seems Biden is speaking for Mitt Romney. From his comments about chaining black voters to his suggestion that the middle class has been "buried," Biden has helped the Romney camp enough that he at least deserves a Romney-Ryan campaign fleece.

Paul Ryan has had an easier time sublimating himself to his boss's agenda. Though he is new to the crucible of a national campaign, he has not caused Romney a single headache. When his positions have come into conflict with Romney's on the hot-button issues of Social Security, Medicare, and abortion, Ryan has fallen in line. He has made the transition from policy wonk to attack dog nicely, as demonstrated by his speech at the Republican National Convention. He has only one more hurdle left, and if he clears it Thursday night, he will either be the vice president or the front-runner in 2016.

Most of us who follow politics say the vice presidential debate is meaningless. Voters base their votes on the name at the top of the campaign sign. That is true. But in this campaign, where merely the clumsy repetition of a months-old talking point can control a few news cycles, surely the debate performance of the fellow who is one heartbeat away from the presidency has the potential to shake things up. If nothing else, the debate will provide us with language and moments to discuss the existing themes of this election.

Here's how either Ryan or Biden may affect the race (and thereby gain a place in vice presidential debate history): if they commit a confirming blunder. What is this particular species of gaffe? In the veep debate, I'd define it as a statement or action that underlines the most negative stereotype about the top candidate.

Of course, we have been told that this campaign is rife with blunders, gaffes, and missteps. So what is not a confirming blunder? Big Bird, for starters. In the first debate, Mitt Romney made a joke that Big Bird would lose federal funding if Romney becomes president. President Obama says Romney's priorities are misplaced. He doesn't care about hurting kids, and the amount he would save by firing Big Bird is minuscule--which really goes to show you how much he is not telling us about what he plans to cut. Romney uses Big Bird on the stump, too. The president wants to protect Big Bird, he says; I want to protect American families. The tweet-a-tweet over the Sesame Street character confirms nothing but the pre-existing views of both sides.