(Image Credit: Joe Raedle/Getty Images)

'Top Line'

The remaining four Republicans vying to challenge President Obama in the fall will gather on a debate stage tonight for the first time in several weeks, and the last time before Super Tuesday.

There is a lot on the line for each of these guys, and ABC News' Rick Klein and Yahoo! News White House correspondent Olivier Knox offer some unsolicited advice.

Rick Santorum arguably has the most on the line tonight. He really has never been in the center of the storm in these debates, having only risen to the level of a serious challenger in recent weeks. What should he do?

Santorum: Go Blue or Go Home, Knox advises.  The former Pennsylvania senator should lean hard on his blue-collar roots, a good way to connect with Michigan voters.

Don't get angry, lose your temper and get caught up in social issue debates. These will be the rat holes Santorum must avoid and, surely, front-runner Romney and the moderator will be looking to see if you head in that direction.

Mitt Romney: Pick a fight with someone, anyone.  Romney can't afford to lose the Feb. 28 Michigan primary and recent polls have shown Santorum surging in Romney's home state.  So Romney needs to look strong and presidential and assure his party base that he has what it takes to take on Obama.

But don't go placing $10,000 bets, governor.  That move in a previous debate and other debate clunkers have shown you to be out of touch with middle-class Americans. Watch your step.

Newt Gingrich:  This may be your last chance but, of course, we've said that before. Gingrich has to make some noise, perhaps attack the media, his frequent target, rattle Romney and shake up Santorum. If he has another ho-hum debate performance, he could be done.

And Ron Paul: You're still a long shot, but are you fighting to challenge the party's orthodoxy and tweak its establishment, or looking to influence the convention's speaking schedule? Without any debate missteps, you'll be doing all of that.