We hoped that they would be right, that they would measure with accuracy the value of our lives against the enormity of the national interest that might call upon us to go into harm's way.
Enormity (Websters): an outrageous, improper, vicious, or immoral act
Enormity (Cambridge): extremely evil act or the quality of being extremely evil
The origin of 'enormity' is similar to 'enormous,' that is, large in excess, though the meaning grew from the idea of being significantly departed from the accepted, moral norm. I really hope that he meant the significance or importance of national interest, and needs a new speech writer. The alternative is that he believes the national interest of this country has been evil since the time of the Korean conflict (which, despite his accolades to Eisenhower, is technically ongoing).
Just my $.02 on tonight's speeches... UPDATE Ok, a quick search shows that he does seem to know what the word means:
Webb said the enormity of what happened there is, "almost beyond description." But he says the government hasn't "really stepped forward to do anything about it."