I never understood why Senator Geary left the hearing when Michael was testifying. Obviously he's indebted to the Corleones for helping him out with the dead hooker, so wouldn't they have wanted him to stay? This way he could maybe throw some easier questions that Michael could quickly answer and look good, or if the other senators are turning up the pressure on Michael, he could do something to help break it up.
He had to leave the proceedings in order to preside over a very important committee, his own committee.
But before he left, he did want to say that the hearings on the Mafia are in no way whatsoever a slur upon the great Italian people. Because he can state from his own knowledge and experience that Italian-Americans are among the most loyal, most law-abiding, patriotic, hard working American citizens in this land. And it would be a shame if we allowed a few rotten apples to give a bad name to the whole barrel. Because from the time of the great Christopher Columbus up through the time of Enrico Fermi right up until the present day, Italian-Americans have been pioneers in building and defending our great nation. They are the salt of the earth, and they're one of the backbones of this country.
:mic drop:
I think his little homage speech to the great spirit of Italian-Americans was all Geary could do to help Michael out in terms of damage control and to not sit idly by as the committee grilled Michael. On top of that, you don't want your sources to look like their in your pocket so it wouldn't make sense for Senator Geary to try and pretend to grill Michael over anything, particularly the inner-workings of Nevada gambling since Geary represents that state.
I also think it was Geary who tells Michael and Tom that the Feds had Pentangeli hidden away awaiting testimony. I have no proof of this but if you know anything about US Lawmakers is that they are privy to inside information well before it is made public.
To stay and feed Michaeleasy questions would draw unwanted attention and suspicion to him and would deprive him of the opportunity to win some nice points with his speach...