George Bush, on why he vetoed S-CHIP:

Q I wanted to ask you about S-CHIP and why you even let that get to a situation where it had to be a veto? Isn’t there a responsibility by both the President and congressional leadership to work on this common ground before it gets to a veto?

THE PRESIDENT: Right, as I said, we weren’t dialed in. And I don’t know why. But they just ran the bill, and I made it clear we weren’t going to accept it. That happens sometimes. In the past, when I — I said, look, make sure we’re a part of the process, and we were. In this case, this bill started heading our way, and I recognize Republicans in the Senate supported it. We made it clear we didn’t agree. They passed it anyway. And so now, hopefully, we’ll be in the process. That’s why the President has a veto. Sometimes the legislative branch wants to go on without the President, pass pieces of legislation, and the President then can use the veto to make sure he’s a part of the process. And that’s — as you know, I fully intend to do. I want to make sure — and that’s why, when I tell you I’m going to sprint to the finish, and finish this job strong, that’s one way to ensure that I am relevant; that’s one way to sure that I am in the process. And I intend to use the veto.

That certainly explains a lot. See also Dan Froomkin.