Don't underestimate your enemies, guys. Even if we think Biden is a doofus, some of the operatives around him presumably aren't. Also, historically, incumbants have tended to fair better on second debates than first ones, which tend to favor challengers.
I hadn't even considered one (or both) bailing on the debate (medical condition, family, ginned-up national emergency, whatever), but I seriously doubt they'd do so. They may as well try floating up Bev Perdue's trial balloon of cancelling the elections, because bailing out like that (esp after the last performance) would reek of exactly that.
I do tend to think Biden is marginally better talking off-the-cuff than Obama, if for no other reason his experience, but that's damning with faint praise. I've only seen Ryan's speeches once or twice, so I'm not sure how good he is in a debate setting, though I agree with most of his policy positions.
The other factor to consider is what/how the MSM/moderator shenanigans will play out.
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