Former defense secretary Robert Gates’s memoir was released this month. (Paul J. Richards/AFP/Getty Images)

Former defense secretary Robert M. Gates on Monday substantially softened suggestions in his new tell-all memoir that President Obama may have opposed the U.S. troop increase in Iraq in 2007 for political reasons.

“What I say in the book was that the president conceded a lot of opposition to the surge had been political,” Gates said on NBC’s “Today” show during a promotional tour for his book, “Duty,” which will go on sale Tuesday. “He never said that his opposition had been political. And, in fact, his opposition was consistent with his opposition to the war all along.”

President George W. Bush sent more than 20,000 additional troops to Iraq in 2007 as part of a controversial strategy to reduce violence in the country, which the United States had invaded four years earlier. Obama, who had always opposed the war, criticized the surge as a presidential candidate, as did Hillary Rodham Clinton, his chief rival for the Democratic nomination. Many analysts credit the surge with helping to stabilize Iraq.

In his book, Gates writes that Clinton, who as a senator had voted to authorize the war in 2003, acknowledged that her opposition to the surge had been because of her primary campaign against Obama. He added, “The president conceded vaguely that opposition to the Iraq surge had been political.”

Gates then wrote that he considered Clinton’s and Obama’s concessions disappointing, saying, “To hear the two of them making these admissions, and in front of me, was as surprising as it was dismaying.”

The book offers wide-ranging criticism of how the White House carried out foreign policy in the first two years of the Obama administration and raised questions about whether Obama fully embraced his strategy of sending more troops to Afghanistan.

The president refrained from criticizing Gates during his first public remarks on the book Monday, defending his administration’s Afghanistan policy and saying that “war is never easy.”

“What’s important is that we got the policy right, but that this is hard, and it always has been,” the president said during remarks at the White House. “Whenever you’ve got men and women that you’re sending into harm’s way, after having already made enormous investments of blood and treasure in another country, then part of your job as commander in chief is to sweat the details on it.”

Obama said that Gates “was an outstanding secretary of defense, a good friend of mine, and I’ll always be grateful for his service.”