"It is," Gibbs said during the daily media briefing, "one that I will be forever thankful and grateful for."
Gibbs announced Wednesday he is leaving President Obama's White House to join the president's re-election campaign with David Axelrod and Jim Messina. He is expected to leave some time after Obama's State of the Union address.
Obama called Gibbs a close friend, "one of my closest advisers and an effective advocate from the podium for what this administration has been doing to move America forward. I think it's natural for him to want to step back, reflect and retool."
While his departure will present challenges and opportunities to the White House, Obama said Gibbs will still play an important role with the Obama team.
Gibbs said having new voices in the White House is good for the process, "even as people like David Axelrod and I go outside of the building and have a chance to talk to the president and people here with a slightly different perspective."
The press secretary said he didn't reach his decision easily, but it was a "very natural time" for him to recharge a bit.
Several media outlets reported Gibbs deputies Bill Burton and Josh Earnest have been mentioned as successors, along with Jay Carney, a spokesman for Vice President Joe Biden.
Other staff changes could be announced as soon as Friday, senior officials said.
Obama has narrowed the list of contenders for White House chief of staff -- replacing Rahm Emmanuel, who returned to Chicago to run for mayor -- to interim boss Pete Rouse and former Clinton Commerce Secretary William Daley, two officials told CNN Wednesday.
Obama likely will name former Clinton official Gene Sperling, now a Treasury Department counselor, to replace Lawrence Summers as chairman of the National Economic Council, aides said.
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