Actually, he doesn't know it. Lindsey Graham doesn't have the vaguest frakkin' clue whether you or I or anyone else is "talking to the terrorists" - any more than John McCain had the foggiest notion that he was hobnobbing with "terrorists" when that photo of him was taken in Syria recently.
Similarly to the situation with McCain, Graham is just "taking a flyer" - he's ignorantly guessing while banking on the statistical probability that the person(s) he was addressing was not, in fact, "talking to the terrorists."
This is why Graham & McCain are so full of shit that they squeak - they profess certainty when in fact they (quite literally) do not know whereof they speak.
Well, then, you could say that about most people in government. Guess what, friend, I don't think they're stupid at all. I think they know exactly what they're doing. Lindsey Graham is one of them and he is helping to indoctrinate the masses. It's not stupidity that leads him to do this. Knowledge is not all. It takes a good heart to truly care enough not to be sucked into the machine. Obama is not stupid, he is evil. Bloomberg is not stupid, he is evil. Romney is not stupid, he is evil, etc. Lindsey Graham is not stupid, he is f***ing evil.