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WASHINGTON — President Obama called Vice President Biden "one of the best vice presidents in our history" on Thursday, days after a newly published book revealed that the White House had done polling on swapping Biden for Hillary Rodham Clinton for his re-election bid.

In an interview with Chuck Todd of NBC News, Obama left some wiggle room as to whether he knew that his aides — as reported in Double Down: Game Change 2012 — explored the possibility of the swap. Adding Clinton to the ticket didn't materially improve Obama's odds, and the idea of a swap was scrapped, authors Mark Halperin and John Heilemann wrote.

Asked about the book's revelation, the president didn't deny that idea was explored.

"I am in charge of 2 million people in the federal government," Obama said. "So people do all kinds of stuff. Some of it they clear with me. Sometimes they're trying to figure something out — particularly on the political side. And I'm not somebody who delves into polling and all that data."

He said, "Here's the one thing I can say for certain: that if they had asked me, I would have said there is no way that I'm not running again with Joe Biden."

Obama went on to call Biden a friend and one of his most important policy advisers.

"When my back's up against the wall, he has my back," Obama said.