In his memoir "Duty," Gates recalled his disgust after Reid said in 2007 that the Iraq war had been "lost."
"I was furious and shared privately with some of my staff a quote from Abraham Lincoln I had written down long before. 'Congressmen who willfully take actions during wartime that damage morale and undermine the military are saboteurs and should be arrested, exiled or hanged,' " Gates wrote.
(Lincoln didn't actually say that.)
Gates picked up that thread during an interview Wednesday on "Morning Joe."
"When you have somebody like the Senate majority leader come out in the middle of the surge and say, 'This war is lost,' I thought that was one of the most disgraceful things I had heard a politician say," Gates said.
"That sends a riveting message to kids who are putting their lives on the line every day that they're doing it for nothing, and that was absolutely not the case."
Reid's office declined to comment.
This post has been updated.