Seems that the reason why they insist on not understanding is because that way they are able to say that Bush is lying. It is why they showed that portion on the tape outside the hearing. That along with gonzales saying that he would advise congress asap if the President was involved in anything illegal. Showing of that tape was to help the 'people' understand that both Bush and Gonzales are liars. I wonder who it was who advised that the tape could NOT be shown.
Specter is the chairman so the decision would be his, I believe.