The most common view of VP debates are that they have little to no impact on the race. However, that may not necessarily be the case tonight for several reasons...
1. Finally, the media will stop talking about the Obama collapse in the first presidential debate, but what will the new story line be? It is vital for Biden to stop the bleeding if they want to stop the Romney momentum. A perceived draw by a vast majority of Americans should effectively do this if Romney's momentum is entirely linked to the first presidential debate. In fact, a perceived draw by many could be considered a win for Biden.
2. Will Paul Ryan bring the Libyan debacle? If he does so in an effective manner and Biden does not have a conversation stopping retort to it, this issue will come front and center in the eyes of the American people for the first time for many voters. If one of the hot topic coming out of this debate is Libya, then I expect the momentum to continue for Romney.
3. This could very well be a ruthless, hard hitting, accusation throwing affair tonight. Remember, Biden did not have this choice in his debate four years ago against Palin, as it would have been considered offensive and disrespectful to many having this type of tone against a woman opponent. Also I think the Obama camp is anxious to show the democrat base that they have learned their lessons from the first debate. The big question will be how Ryan responds. Conventional wisdom says that when things are going good don't mess things up and take a conservative approach. I think this would be a huge mistake for Ryan to make. He must not only address the continual attacks from Biden, but shift back to the offensive. Ryan can not afford just to play things safe tonight. Doing so will likely make Biden the big winner and squelch Romney's momentum.
4. Assuming this is a feisty debate... The danger for both candidates is that if one of them is perceived to have crossed the line of professional demeanor and basic decency. Suddenly, the story line for the next several days is set and it would not be pleasant.
5. Will this debate turn intellectual at times and open up the door for Ryan to press Biden on some issues that could bring embarrassment to the Obama campaign? -OR- Will Ryan come across as Mr. Professor and portray a know it all attitude?, which would likewise hurt the Romney camp.