Because he says stuff like this:
"At the Senate Foreign Relations hearing, Barbara Boxer related the story of how, a month ago, Iranian prez Ahmadinejad traveled to Iraq and got kissed on the cheek by Iraqi prez Talabani. Then she asked, in a pained tone,
"BOXER: After all we've done, now Ahmadinejad is getting kissed on the cheek, and Bush has to sneak in? Isn't it true that, after all we've done, Iran has gained Iraq?
"CROCKER: It's a mixed bag. Iran by no means has it all its own way in Iraq.
"BOXER: I give up. It is what it is. They kissed him on the cheek! He [Ahmadinejad] had a red-carpet treatment.
"CROCKER (sheepishly): When the vice president was in Iraq, he got a very warm reception!
"BIDEN: Did he get kissed?"