As torture, to me waterboarding is borderline, but finding the higher moral ground is not. To me, the lives of the many innocents is worth more than the physical comfort of someone hellbent on killing them.
Someone offered the nuke in a city of 100,000 scenario and waterboarding the perp to find the nuke. Could you tell any of those 100,000 people that you've taken the higher moral ground and are going to let them die so you don't waterboard another human? I'm sure they'd all thank you and feel good about your conscience.
It's a collosal Catch-22. If you take the moral high ground & lose 100,000 citizens then you are the worst commander-in-chief in history & will be derided, impeached & perhaps convicted of deriliction. If OTOH you rough-up/torture to save 100,000 citizens then some of those same citizens will want to bring the CiC up on War Crimes some years after the fact. If I were president I'd take my chances on the War Crimes whenever I was in a "grey-area".
Three responses:
1. Since waterboarding is a method short of torture, I would not forbid it in such extreme circumstances, subject to controls, as I have described above.
2. If you are asking about what I would do personally, I would do a heck of a lot more than that, if I could assemble the proper tools. But I am a bit of a hot-head. I don't write policy for the US military, and they haven't asked my opinion.
3. Even if a hard-and-fast policy against waterboarding existed, as long as the Presidential power of Pardon exists, nothing is absolutely illegal. If it saved 100,000 lives, you could be pretty sure the President would see your side of things.