Al GoreAl GoreTrump’s isolationism on full display at international climate talks Overnight Energy: Trump officials defend fossil fuels, nuclear at UN climate summit | Dems commit to Paris goals | Ex-EPA lawyers slam 'sue and settle' policy Al Gore: A new president in 2020 could keep US in Paris agreement MORE said ahead of Wednesday night's presidential debate that Mitt Romney, who is trailing in key swing states, must take risks and walk a fine line of being aggressive without appearing “mean” towards President Obama.

“I think he has to be aggressive without seeming to be aggressive. I think it is a tricky act for him to pull off,” Gore said of the GOP presidential nominee on Current TV, a network that he co-founded.

“I think he has got to take some risks and I am sure that he has been practicing this art ... of being aggressive without running the risk of seeming mean,” said Gore, who is anchoring the network’s coverage of Wednesday night’s first debate between Obama and Romney.

The former vice president knows the stakes.

His performance in a 2000 debate against Republican George W. Bush, when Gore sighed audibly and rolled his eyes, was seen as hurting his candidacy.

Gore said that Romney faces a tricky task of taking the fight to Obama in the debate without being “over the top,” given Obama’s personal popularity.

“He is going to try and be aggressive, I am certain of it,” Gore said ahead of the Denver debate between Romney and Obama. “Advisers in one ear are saying, 'be aggressive, you have to take it to him,' and in the other ear they are saying, 'be a nice guy, this president’s popularity ratings are high, you can’t be really too over the top and come off unlikable.' ”