An unexpectedly sullen expression. Could he possibly have considered it a nuisance to be bothered with a simple terrorist act at such a time?
On the other hand, maybe he conceived his whole plan of a war against terrorism within these few minutes? Might explain some things.
And then perhaps he was just asking God what to do (some call it praying). Which would explain a whole lot more.
I mean, please give the man some credit. After all, he's not Superman, even if he thinks so.