That is the question that every Democratic should ask when answering criticism of the way this Administration used intelligence to justify the war. If they didn't do anything wrong, then they should welcome an investigation because it would convince Americans that there was no misuse, no manipulation of intelligence to justify the war in Iraq.
This question seems to me to be so simple as to defy belief. Any Democrat who appears on a talk show, or who writes letters to the editor, or who answers questions about this topic from reporters should be raising this question.
The Republicans may try to say something like "well, raising these questions distracts us from the war efforts and discourages our troops". The answer is that the suspicion held by a majority of Americans that the Administration manipulated the intelligence hurts our war effort more. The way to put this issue to rest is by a full investigation so we can move on, which is something like what they said during the impeachment of Clinton.
Of course, since this administration doesn't want an investigation, nothing we say is going to be met by anything other than attacks on our patriotism. That's fine, because the audience isn't the administration, or even Republicans, it is the significant number of Americans who don't identify with either party, or if they do, are very loosely identified with either party.