Investigations
We went through all this here in excruciating detail a few years back. People spent a long time breaking their backs trying to pin a crime, or even an outright lie, on Bush. Eventually the liberal consensus was reached that even if Bush didn't actually lie, he somehow created a penumbra of impressions designed to make a false picture in the mind of the gullible American public. The discussion pretty much stopped there.
As for investigations, there was an investigation. It didn't come up with the answers the Left wanted, i.e. and impeachment, so it was dismissed and forgotten. Maybe you can get some information out of it.
Cheney is right.
Read the Duelfer Report. Or, to save time, just go to the key findings.