WILLIAMSBURG, Virginia: With his hopes of a second term under threat, US President Barack Obama will seek to summon fresh energy on Tuesday (Wednesday in Manila) to thwart Mitt Romney’s momentum in their crucial second debate.

Republican Romney’s assured performance in the first encounter two weeks ago in Denver, and Obama’s own lifeless showing, dented the president’s polling numbers, leaving the race effectively tied 21 days before the election.

Obama has admitted that he had a “bad night” in Denver. Another one at Hofstra University on Long Island, New York, would be deeply damaging and significantly increase his chances of suffering the historic stigma of a one-term presidency.

Romney must prove that his surprisingly assured showing in Denver was not a fluke and faces a higher bar of expectations, as his aides bu-sily talk up prospects of an Obama comeback in hopes of managing post-debate news coverage.

On the eve of the debate, a dramatic intervention from Hillary Clinton, Obama’s former bitter Democratic Party foe, and now his secretary of state, may have defused one of Romney’s most damaging attacks.

Clinton said that she—and not Obama or Vice President Joe Biden—bore responsibility for any security lapses before the attack on the US consulate in Benghazi, Libya on September 11, which killed US ambassador Chris Stevens.

“I take responsibility,” she said, according to CNN and Fox, which interviewed her during a visit to Peru.

Romney and his vice presidential nominee Paul Ryan have claimed that the Benghazi raid, and the administration’s shifting accounts of it, are symptomatic of an “unraveling” of Obama’s foreign policy.

The president was likely to be cross-examined on Libya in the debate, but the statement by Clinton, who has political capital to spend and is very popular, may have given him badly needed room for maneuver.

Obama has been largely out of sight since Saturday, when he flew to the historic colonial-era city of Williamsburg, Virginia, for an intense debate camp, lent added importance by his limp 90-minute stumble in Denver.

Aides promise a more aggressive and energetic Obama will show up, and have signaled the president will challenge what he calls Romney’s “extreme makeover” of sharply conservative positions to woo moderate swing voters.

“Mitt Romney will say and do anything, regardless of whether it’s true, to become president,” Obama campaign spokesman Jen Psaki said.

An Obama advertisement released on Monday (Tuesday in Manila) highlighted what his campaign calls the “Real Romney,” contrasting previous positions on abortion, student loans, cutting taxes for the richest Americans, Iraq and immigration.

In a positive ad airing in battleground states, Americans from “Main Street” offered testimony on an improving economy.

“Stick with this guy, he will move us forward,” one man says in the ad.

Obama has spent many months and millions of dollars arguing Mitt Romney does not care about the middle class. In the debate, he faces pressure to prove it, before an audience of voters in the town hall-style debate.

CNN’s Candy Crowley will moderate the showdown, with questions posed by about 80 undecided likely voters selected by polling group Gallup.

Some analysts have speculated that the more collegial setting could hamper Obama’s efforts to challenge Romney more aggressively than in Denver.