The President of the United States is a target, and has special security concerns which are often burdensome, every time he goes out in public, especially now that we are at war. He didn't attend his daughters' college graduation because of it, it does not mean he doesn't love them or wish he could have been there. It means he thinks more of who he would be inconviencing than he thinks of himself.
If you are trying to make the point that Bush is a bad Christian because he doesn't attend services in a public church every Sunday, give it up. It just isn't true. You do not know that Bush does not worship PRIVATELY with others at Camp David or in Crawford.
I am assuming you are not trying to start a war between Catholics' views of services and Protestants' views of services. In the Protestant view, PUBLIC Sunday worship is NOT mandatory, since salvation rests on faith, not works. Protestants realize Catholics believe differently about this. Bush is a Protestant, not a Catholic, that is no shock to anyone.
Only on FR could a post about Bush shaking up establishment Washington turn into an issue between Catholics and Protestants.
If that's his understanding, which I believe it is, then his decision would not be sinful. However, as a matter of fact, Christians are obligated to attend Mass every Sunday. I've presented my arguments here. You're free to present yours.