Who does Zawhiri fear most?

I would say that Zawahiri and Bin Laden fear Obama more than God. They feared Bush more than God too. They talk tough, but live in hiding. Who are they hiding from and why? They are hiding because they do not want to die. They are hiding from that which they fear. They fear the US. So when the two of them weigh their faith in God and their fear of the US, the scale tips toward fear of the US. Obama does not live in hiding. Neither did Bush. America is confident while her enemies live in holes, sitting next to rusty guns used as props, making pronouncements. America knows that Zawahiri and Bin Laden, and their followers hate it.
So again why do they hide? They do not want to die? If they are confident in their service to God then why should the fear? Maybe they fear the US and God. They fear the US for its ability to kill them and they fear God in His ability to lay vengeance upon them for killing in His name.