The comments about Tenet should exonerate Bush even in the minds of liberals, if they are true and if there really were no WMD's. But liberals want Bush to be guilty so those comments won't even exonerate Bush in the Liberal mind even if WMD's are eventually found, as I believe they will be.
BTW, just because they haven't been found in mass quantities yet, does not mean they won't be and it also does not mean that Tenet was wrong. Bush probably believes they were there, are yet to be found and in that case sees no justification for firing Tenet.
What you said (that Bush hasn't given up on finding WMD and so hasn't cause for firing Tenet) is certainly possible.