Fox News reports that in connection with passage of the 2006 Military Commissions Act, Sen. Ted Kennedy proposed an amendment that would have expressly defined "waterboarding" (among other indignities) as a grave breach of Common Article 3 of the Geneva Conventions. The Amendment lost, 46-53.
That is, the same senate that wants Mukasey to say waterboarding is unambiguously illegal in all circumstances declined to make it unambiguously illegal in all circumstances. I realize that the senate was in Republican hands then and it is in Democratic hands now; I realize if the vote were retaken today, the Amendment would have a better chance of passing. But the stubborn fact remains: it didn't pass – it lost.
Of course, you may have to waterboard Senators to get them to admit it.