The right's theory on this seems to be based on a novel standard for truth-telling whereby if any of Bush's statements (about, say, chemical weapons) turn out to have been true even in part it follows that he's not a liar. According to the standard theory of truthfullness, an honest case for war is one in which all the elements are true.

I think Matt's being a little non-specific here. An honest case for war is one which the president makes in good faith, using claims (s)he justifiably believes to be true. That is, a case for war could be factually wrong and still be honest. (Or factually correct, and still dishonest, for that matter.)

So now we have a subdefintion issue. How does someone "justifiably believe" a claim to be true? Well, that's classic epistemology, right? It's the "justified" and "belief" parts out of the "justified true belief" standard definition for knowledge. What would have made Bush's claims about the WMDs "justified beliefs"? a) If they were supported by a proper procedural evaluation of the evidence (they weren't) and b) if he really believed his own claims. Since none of us can speak to b), it's not worth considering either way. Regardless of b), since Bush's claims were intentionally manipulated by his own preconceptions, intelligence-organization rejiggering, and outright dishonesty on the part of his advisors, we can certainly conclude that the procedure was flawed, so no, his claims weren't justified, and yes, his case for war was dishonest.

It's important for people to understand that the left doesn't say "Bush Lied" because Bush, despite his best efforts at getting to the truth, turned out to be wrong--we say "Bush Lied" because the apparatus of his Presidency was directed not at finding the truth out about Saddam's weapons, but at convincing us that all of the worst possible things were true so we'd support the war (and by association him).

[Obligatory link to the Gettier dissertation (the shortest philosophy dissertation ever accepted, to my knowledge--and it's incredibly important to boot) here. Skip down to the cases, which aren't represented by symbolic logic, and aren't jargony.]

UPDATE: One sentence version of the above: Bush wasn't "dishonest" because it turned out he was wrong; Bush was dishonest because he didn't care whether he was right or not.