Sen. John McCain (R-Ariz.) said on “Face the Nation” Sunday that — like most Republicans and even some Democrats, including some in the president’s cabinet — he thinks President Obama was right when he said “we ought to go forward, not back.”

But then he went on to say, as Glenn Greenwald tweeted yesterday, that “I think the interrogations were in violation of the Geneva Conventions and the Convention Against Torture that we ratified under President Reagan.”

Now, once you acknowledge that the CIA, at the direction of senior cabinet officials, violated international humanitarian law that requires the United States to prosecute the perpetrators, the only way to justify not investigating is to say that the executive branch of government is above the law — or, put more pragmatically, that it’s politically too messy to investigate senior leaders in the U.S. government.

Republicans didn’t hesitate to investigate when it involved Democratic President Bill Clinton, however, or to bring charges against him for lying about a personal matter. And Congress didn’t turn its backs on the Iran-Contra scandal during the Reagan administration, which led to 14 senior officials charged with crimes, and 11 convictions. And of course the Watergate affair led to the indictment and conviction of senior Nixon administration officials, and impeachment charges against the president. Congressional investigations of sitting and past administrations are far from unprecedented.

So how does McCain explain why we ought to forget the whole torture problem — which led to the deaths of a still-unknown number of detainees in custody, some of whom the CIA still can’t account for — even as he acknowledges that it violated international treaties that legally obligate us to prosecute?

“I think these interrogations helped al-Qaeda recruit,” McCain said yesterday, adding: “the damage that it did to America’s reputation in the world we’re still on the way to repairing.”

Even setting aside the legal requirements, as a practical matter, a public acknowledgment and investigation would seem to be the only way to repair that damages.

As McCain put it: “This is an ideological struggle as well as a physical one.”