Speaking to reporters at the White House, Bush remained cool to such a move, saying Syria needed to get out of Lebanon and Iran needed to abandon its nuclear ambitions.
He pointed out that the United States had offered direct talks with Iran about its nuclear ambitions if Tehran would agree to stop uranium enrichment, which Iran has refused.
So, Bush's idea is that the idea of getting Syrian and Iranian help/diplomatic solutions to the Iraq quagmire is to drag unrelated issues into the conversation. Also, he seems to have the peculiar iddea that the idea of diplomacy is to get the other guys to surrender all of their advantages first, then when negotiations begin, there's nothing left to negotiate over as the other side has already given up everything that motivated the US to begin negotiations in the first place.
Update: "While the administration's defenders claim that it has exhausted diplomatic possibilities..."
I believe that the statement above shows us that diplomacy has not been seriously tried. Bush has no interest in real diplomacy and has never really tried any. The current situation between the US, Iran, Syria and the Iraq insurgents brings to mind a metaphor of Bush flailing about in the water, having gone down for the second time (Third time is normally the last time), the Iranian President Mahmoud Ahmadinejad and the Syrian President: Bashar Al-Assad are passing by in a rowboat. Ahmadinejad takes pity on Bush and extends an oar to him. Bush replies: "Hey!! Why don't you junp in the water and pull me out? What's that? Will I drag you under? You'll just have to take the chance that I'll decide to be a nice guy and not do so. What, your clothes will get wet? $#%#@, just GET DOWN HERE!!!" Surprise, surprise, Ahmadinejad and Al-Assad look at each other, shrug and keep paddling on.