I think this was President Bush's call. He saw it as a political stunt and was not going to play. If the Pres allowed cleland in, this would not be the end of this crap. We'd have other uninviteds showing up all the time..probably the NAACP, for one. I think GWB did the right thing.
It also had the possibility to end up like a Leahy thing too. These people have zero scruples.