Barack Obama has insisted he has faith in the Afghan war mission after former Pentagon chief Robert Gates charged the president with lacking passion for military action and soured on his own troop surge.
In his first public comments on explosive criticisms of his role as commander-in-chief in new memoirs by Gates, Obama said on Monday that he had a duty to constantly question US military tactics and "sweat the details" when sending young men and women to war.
But the president declined to say whether he had been irked by the publication of the book while he was still in office and American forces remained on the battlefield.
Gates sparked a Washington firestorm when he suggested in Duty - to be published on Tuesday - that Obama became disillusioned with the troop surge strategy launched in 2009 by early 2011, and lost confidence in his troop commanders and Afghan President Hamid Karzai.
While praising Obama for his integrity and intellectual approach to matters of state, Gates is reported to have written that the president showed less zeal for military engagements than his predecessor George W Bush.
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"One quality I missed in Obama was passion, especially when it came to the two wars," Gates wrote.
Obama, however, said that he "continued to have faith" in the US mission in Afghanistan.
"Most importantly I've had unwavering confidence in our troops and their performance in some of the most difficult situations imaginable," the president said.
"And that job is not yet done."
The frank criticism from Gates, who served both Bush and Obama as defence secretary, was all the more surprising considering he is known in Washington for loyalty and disdaining the often grubby business of politics.
In an interview broadcast on Monday, the former Pentagon chief complained that the contents of his book, leaked to some newspapers, had been hijacked by those with a political axe to grind.
"I think the book is very even-handed. I don't vilify anybody," he told NBC's Today Show.
"I make it clear, I have a lot of respect for both president Bush and President Obama," said Gates.
He said that "what has been lost in the news media is that I actually agreed with virtually every decision President Obama made" on how to handle the US war in Afghanistan.
But "some people who have a narrative on Obama and the war got out there early with their take on ... what I've written," he told National Public Radio.
Gates, a Washington veteran who also once headed the CIA, made a distinction between Obama and the rest of the White House.
While his criticism of Obama is coupled with praise and respect, Gates makes no apologies for his blunt criticism of Vice President Joe Biden and of the White House staff.
"Well, I had a lot of battles with those folks," he told NPR, referring to members of Obama's National Security Council staff.
