NEW YORK — If President Barack Obama wins re-election in three weeks time, he will begin his second term heavily in debt to Bill and Hillary Clinton, one-time tormentors turned power couple protectors.

As Obama headed to New York for a crucial debate against resurgent Republican challenger Mitt Romney, the Clintons, the dominant Democrats of the last 20 years, were again stealing the headlines.

Taking a hit Romney may have lined up for Obama, Secretary of State Hillary Clinton took the blame Monday for shortcomings in the handling of an attack on the US consulate in Benghazi that killed four Americans.

Her comments, in Peru, may have taken some of the sting out of Romney's possible attack and marked the administration's most emphatic effort to quell a political storm over Libya that threatens to hurt Obama's re-election bid.

The 11th-hour pre-debate intervention also prompted new questions over the motives of the Clintons in embracing their former foe, including: will Hillary demand payback from Obama if she runs for president in 2016?

Republicans though pinned the Benghazi blame on Obama, recalling the ad Clinton ran in the 2008 Democratic primary, questioning whether her relatively inexperienced rival was ready for a national security crisis.

"I think it's the 3 am call, right? I mean, the buck stops at the White House. That's what Hillary Clinton said back in 2008," Republican party chief Reince Priebus told MSNBC.

With a wink and a smile, Clinton declares she is already "out of politics," but her popularity makes her decision to accept the Benghazi fallout for Obama on the eve of a make-or-break debate a distinctly political act.

Bill Clinton, the 42nd president, was waging another tussle for his Democratic successor, rebutting Romney's tax policy in the folksy drawl he used in last month's acclaimed Democratic National Convention speech.

In a campaign video, the snowy-haired veteran made the kind of forceful case that was beyond Obama in the first debate -- a point not lost on one of the ex-president's chief antagonists, former Republican House speaker Newt Gingrich.

"You have to admire the Clintons. Bill and Hillary Clinton have done more to re-elect Barack Obama than Barack Obama has," Gingrich told Fox News.

Costas Panagopoulos, a political analyst at Fordham University, who once worked in Hillary Clinton's senate office, agreed the former first couple had made a big effort to help Obama.

"The president will win re-election or lose re-election on his own record and his own merits," he said.

"But if he is re-elected, he will owe a great debt to the Clintons."

Bill Clinton, who has lent his aura of economic credibility to Obama, will hit the campaign trail again in Ohio and Wisconsin this week.

The Clinton effort for Obama is all the more remarkable considering the bitterness spawned by his 2008 primary battle with Hillary.

Obama, whose campaign was once dismissed as a "fairy tale" by the former president, blocked what would have been a remarkable Clinton restoration, eight years after they left the White House.

Clinton was also furious when some Obama backers said he had played the race card.

The thaw began when Obama shocked his inner circle by asking Hillary, then a New York senator, to join his "team of rivals" cabinet.

Even now, few people suggest that the Clintons and Obama are friends, though the president and his secretary of state and her husband show mutual respect.

As for the Clintons' motives, they remain open to debate.

Given Hillary's narrow defeat to Obama and support of 18 million primary voters in 2008, talk of a second presidential campaign is never far away.

Could the former first lady be courting Obama's supporters to bolster her own coalition, knowing she will be the Democratic favorite four years hence?

Some Clinton-watchers doubt the retiring secretary of state, who will be 68 in November 2016, wants another shot, and say her legacy would be sullied if she lost.

Much may depend on political conditions, but the Clintons have towered over Democratic politics for so long that many in Washington cannot believe their ambition is slaked.

A less Machiavellian explanation is that the Clintons simply want Obama to win, as a bulwark against the conservatism they spent their lives fighting.

Bill Clinton must also be luxuriating in the sight of Obama, who was once sniffy towards his 1993-2001 administration, now gushing with praise.

A former Clinton campaign aide said on condition of anonymity, that the ex-president was in a "no-lose" situation.

Should Obama tumble to Romney, Clinton would get credit for helping Obama and would still be known as the only Democrat to win two terms since World War II. Memories of his age of prosperity would grow just a little more golden.

If Obama wins, the ex-president will guarantee himself a place in the history books alongside the man who he once believed stole the Clinton crown.

USA Today columnist DeWayne Wickham suggested that hurt over the race row may also be driving Clinton, once known as America's "first black president" because of his affinity with African Americans.

"If Clinton plays a key role in delivering the winning margin of voters to Obama, an overwhelming number of blacks -- and many historians -- will see him as one of black America's greatest friends," Wickham wrote Tuesday.