It's about the politicaly smartest position Bush could take. I don't know whether it is intentionaly smart or it just works out that way. By saying he would sign the ban if it came to his desk, he wins points with the "soccer mom" crowd.... who, out of ignorance, believe it somehow makes thier kids safer. But Bush knows it isn't going to get to his desk ....therefore he doesn't have to loose points with us gun owners. He's not actively pushing it and he's not actively opposing it...he's just letting it whither on the vine. That's a savvy position. The real test will be to see what happens next year.
Everyone credits the Republican wins in the '90's with the institution of this ban.
No matter how the Liberal Dems or Liberal Republicans feel about the ban, they risk a backlash if they support its extension in an election year. There is no way to know how severe the backlash would be, but do they want to risk the potential will equal the '90's protest or exceed it?
We'll find out.