On Election Night 2012 after clinching a second term, President Obama hailed Joe Biden as "the best vice president anybody could ever hope for."

But a new account of the year leading up to the election, detailed in the book "Double Down," reveals that many of Obama's closest aides weren't always as convinced.

In late 2011, several top Obama campaign officials secretly considered a VP swap for Hillary Rodham Clinton, convening focus-groups and commissioning opinion polls to determine whether the president could get a boost among voters.

"It was a very difficult political year and so my sense was we ought to look at everything here because … it was a very difficult period politically," former White House chief of staff Bill Daley told CBS "This Morning" on Friday.

"But not for a moment did, as far as I know, any of the senior people including myself think that that was a good idea, or needed to be done, or should be done, or whether the president would ever even seriously consider it if you thought it was the right thing to do," he said.

Still, as "Double Down" authors Mark Halperin and John Heilemann tell it, "Biden had dodged a bullet he never saw coming - and never would know anything about, if the Obamans could keep a secret."

Daley said today he believes neither Biden nor Clinton knew that aides were quietly researching the merits of a VP change. He and other former campaign colleagues also insist the idea never reached President Obama.

"I know for a fact that President Obama never considered this; never thought about it; never entertained it," White House spokesman Jay Carney told CNN. "The vice president has been a partner of his from the 2008 campaign on. He's been an excellent governing partner and an excellent campaign partner."

"Anybody who would have brought this idea in to the president in the Oval Office, in my opinion, probably would have been thrown out immediately," Daley said.

One reason the idea never reached Obama is that the internal research concluded that Clinton would not have made a substantial positive impact on the ticket, Halperin and Heilemann report.

"The truth is that any research that was done confirmed the fact that that was not an issue that the voters cared about or thought that should be done," Daley confirmed today.

A Gallup poll from June 2013 found 44 percent of Americans hold a favorable view of Biden, with 44 percent having an unfavorable opinion.

Hillary Clinton has enjoyed higher favorability ratings in recent years, in part because of her apolitical work as Secretary of State. An Oct. 2 Quinnipiac University poll shows 56 percent of Americans have a favorable view of Clinton, compared to 36 percent who do not. (The poll did not ask about views on Biden.)

While not disputing outright the account in "Double Down," former Obama campaign aides have downplayed the episode's significance and come to Biden's defense.

"VP swap never in play. Biden's taken on many tough assignments. He's been loyal friend and wise counselor," former senior Obama adviser David Axelrod tweeted Friday. "POTUS lucky to have him."

Late Thursday, just after news from the book broke, former Obama strategist David Plouffe tweeted that there was "never any - any - consideration of VP/HRC switch.

"Not even entertained by the only person who mattered. Or most of us," he wrote. "Back to Halloween."