Call it the retaliation debate because that's what it is.

The vice president wants to do to Paul Ryan exactly what Mitt Romney did to the president, while Paul Ryan wants to do exactly what Romney did–win big.

Here are some do's and don'ts to help them do it.

What the vice president needs to do:

Above all else tonight, Joe Biden needs to stand by his man, President Obama. Basically, that means Biden needs to make the points the president didn't. The easiest example: tie Ryan to Romney's 47% comment.

Being vice-president is a good job, and Biden seems to enjoy it. Tonight he must earn his keep and fight for his political life because it is on the line.

What Republican Paul Ryan needs to do:

Paul Ryan must show voters he knows what it means to be a heartbeat away from the presidency…that he's ready to lead if necessary.

And he must keep the go in the GOP ticket by maintaining the momentum Mitt Romney created. Clear answers and crisp attacks are the way to do it.

Millions of Americans will be watching, many waiting–even hoping–for one of the candidates to make a major mistake.

To avoid a blunder, here's what the candidates don't want to do:

What Biden doesn't want to do:

With the president's poll numbers in free fall, Biden could get a little desperate and try too hard. Don't! You could actually make it worse.

Usually, it's best to be yourself, but that may not be best for you. You know they call you the gaffe machine. Tonight, be sure the engine to that machine is off.

What Ryan doesn't want to do:

Much of what we know about Paul Ryan is what the democrats have told us: that he's a budget cutter with no heart. So Ryan must show sensitivity and absolutely not be scary

A week ago, Republicans were energized and Democrats were depressed. Maybe Ryan will fall short of that, but he doesn't want to fall flat.

No one would have predicted what happened in the presidential debate, so as I get ready to watch the vice-presidential candidates, my biggest "do" is to expect anything tonight. And I'll be surprised if there are no surprises.

Join our Newsletter for the latest news right to your inbox