Okay, here's what I think, and it doesn't reflect too kindly on Bush. The White House would only agree to a 9/11 Commission if it was assured there would be no partisan attacks. So there was a prior agreement,i.e., the Democrats wouldn't trash the Bush Administration, and the Republicans wouldn't trash the Clinton Administration. When Ashcroft mentioned Gorelick's policy, that broke the underlying agreement. Hence, Ashcroft gets taken to the woodshed by Bush.
But that also means that potentially embarrassing facts won't find their way into the 9/11 Commission Report.
I think W is a good president, and I voted for him twice and worked very hard on his campaigns, but I will never understand why he does not call Clinton and the Dems to account. If it were simply a matter of not wanting to appear vindictive, I could understand it.
But the problem is that the Clinton influence lingers - and lingered particularly heavily during Bush's first term, because he didn't replace a lot of Clinton's treasonous appointees - and will be with us until Bush gets the guts to have a serious investigation, root out the moles and outright traitors, and deal with them accordingly.
I don't think there was any quid pro quo. In fact, the WH recognized that it was a political event and were just happy when it didn't degenerate into a food fight. Nobody expected the hearings to produce anything useful.