A difficult political year
Like Carney said, Daley admitted that it was something he considered and that polling and research were done to explore the possibility because it was his job to "look outside the box."
"But in 2011," Daley said, "it was a very difficult political year, and so my sense was we ought to look at everything here because this is a very -- it was a very difficult period, politically."
Polls conducted by CNN at the time showed that the President was struggling politically a year out from Election Day 2012. In the late summer and fall of 2011, Obama's approval ratings hovered around 45%, a 10-point drop from January of that year.
There was much speculation over whether Biden would be on a second-term ticket in late 2011 and early 2012.
Wolf Blitzer wrote on CNN.com in October 2011 that White House sources told him that the President was "very high" on Biden and "deeply appreciates his advice."
He said he asked Clinton, then Secretary of State, if it was something she would consider but she said, "No."
Obama's former deputy press secretary, Bill Burton, told CNN's Erin Burnett in January 2012, "Even privately, President Obama would tell you that one of the best decisions he's ever made in politics was putting Vice President Biden on his ticket."
"He's not leaving the ticket," Burton added.
According to Jonathan Martin, the Times' national political correspondent, the book provides a thorough account of the effort by senior officials inside the campaign and the White House, namely Daley, to measure what effect swapping Clinton for Biden would have on the polls.
The potential switch was a closely guarded secret within the Chicago campaign infrastructure and inside the Oval Office.
Only half a dozen of the President's closest advisers -- including Daley, former Obama campaign chief Jim Messina, and former White House senior advisers David Axelrod and David Plouffe -- knew the change was under consideration.
Messina, Plouffe and Axelrod took to Twitter to push back on the report.
Plouffe denied the White House or the campaign ever contemplated the swap.
"Never any consideration of (Biden-for-Clinton) switch," Plouffe wrote in a tweet.
The move was "not ever entertained by the only person who mattered. Or most of us. Back to Halloween," he added.
Axelrod tweeted: "VP swap never in play. Biden's taken on many tough assignments. He's been loyal friend and wise counselor. POTUS lucky to have him," Axelrod wrote Friday.
And Messina said: "Let me be clear: VP-HRC switch never considered by POTUS or anyone who mattered in the campaign. #sillyseason"
A significant investment
But Martin pointed out that it was, in fact, considered.
Martin told CNN's Anderson Cooper the re-election campaign made a significant investment in finding out whether the move would pay dividends at the polls.
"Campaigns don't spend the kind of money on polling and focus groups unless they're seriously considering something," he said on CNN's "AC360."
He said on the program that he asked Daley whether his then-boss knew about the potential shuffle. While Daley said he doesn't think the President "was aware" of the potential change, the former chief of staff admitted that it's "possible" Obama knew.
Martin added that "Double Down" does not definitively answer whether the political probing reached Obama's desk.
As to whether Clinton knew, Daley said on CBS that if she did know, she "didn't find out from me."