I'll keep this brief.
Katrina killed less than 2,000.
9/11 killed over 3,000.
Without the war in Iraq, another 9/11 would have happened by now. It's all good and well having troops in your own country to prevent terrorist attacks Leonie, but how exactly do troops on the ground prevent planes flying into buildings? Troops in the US would've been wasted on saving Nagin's arse. If a few thousand people had to die to prove what an inept cunt he was, so be it. Better than another 9/11 killing even more people, which presumably Bush would've been slated for too. Let's face it, the knives were out because of how he won the election, who his father is, and his low IQ.
You also act as if the war began AFTER Katrina, what was Bush supposed to do, withdraw troops in mid-conflict? Presumably if he had and millions of Iraqis died in insurgency, he'd have been blamed for that too. As you point out, Katrina was unexpected. Or was Bush supposed to predict it when Nagin couldn't? As it happens the proof is that Nagin's infrastructure wasn't prepared, for any hurricane, it just so happens that he got hit by a particularly bad one and it caused more damage.
Priority-wise Katrina had to rank lower than the war. It would do with me, it would do with any sane President. Perhaps this is why they let men rule the world ladies