Sen. John McCain has made a shocking admission: The Iraq War was a “mistake,” and he’s taking the blame.

In his new memoir, McCain who is battling brain cancer, writes that the Iraq War “can’t be judged as anything other than a mistake, a very serious one, and I have to accept my share of the blame for it,” as Politico reports.

McCain is among the most hawkish Republicans in the Senate and was an ardent supporter of the George W. Bush administration’s decision to go to war with Iraq and a later US troop surge. As Michael Hirsh writes at Politico:

McCain became, in fact, the first supporter of a “surge,” years before Bush and other Republicans did. “I came out of the Vietnam War convinced that frankly we could have won, and we had it won,” he told me in 2014. “Just as I believed we had the Iraq conflict won after the surge — and for which I sacrificed everything, including my presidential ambitions, that it would succeed.”

McCain’s defense of the Iraq War was unwavering, even when it became increasingly clear that the United States’ stated intention of establishing democracy in Iraq was not only unrealistic but would take hundreds of thousands of lives. (If you want more about the neoconservative ideology behind the war, how the Bush administration convinced the nation to get into it, and how it turned out, read Max Fisher’s Vox explainer.)

In 2005, when 66 percent of the country viewed the Iraq War unfavorably, McCain redoubled his commitment to the strategy:

“Securing ever-increasing parts of Iraq and preventing the emergence of new terrorist safe havens will require more troops and money,” McCain said then at an event with the American Enterprise Institute. “It will take time, probably years, and mean more American casualties. Those are terrible prices to pay. But with the stakes so high, I believe we must choose the strategy with the best chance of success.”

The casualty counts for the Iraq War are somewhere between 150,000 and 460,000 and have contributed to the deep instability in the region, which, as my colleague Jennifer Williams explains, is “one of the conditions that allowed ISIS to rise in the first place.”