As race shifts, Biden gets task of scuffing Romney

"This is a man who can give an entire speech about the wars America is fighting and never use the word 'victory,' except when he's talking about his own campaign," Palin, then the Alaska governor, said in her national convention speech.

But at this stage of this campaign, Biden has no peer who can easily command attention and speak with the full weight of the campaign. Romney, who still lacks the needed delegates to rightfully call himself the GOP nominee, is probably months away from picking his own running mate.

President George W. Bush enjoyed a similar two-on-one advantage for many months of his second-term bid in 2004, with Vice President Dick Cheney at his disposal. Cheney publicly doubted Democratic nominee John Kerry's resolve on national defense, but the vice president didn't play a sustained role in criticizing the rival nominee this early on.

"If you go back and read a lot of the speeches, you will not find (Kerry's) name very much," said Sara Taylor Fagen, a Republican strategist and White House political adviser in Bush's administration. "It's a little surprising that they've gone so hard so fast. To some degree, you want to keep the president and the vice president elevated as long as possible."