I believe you guys are probably right. This is essentially the same tack he took with McCain-Feingold. Opposing McCain and the Democrats was politically difficult, so he simply announced that if it reached his desk he would sign it. This put the onus on the Repubs in congress. They weren't willing to take the heat, of course, so they passed it, Bush signed it. It turns out to be worse for the Dems than for the Repubs, and the Dems are already violating it, and as of a day or two ago, the Supremes are going to throw it out.
It may be that he is counting on it dying in committee, thus eliminating it as an issue, or he will sign it again eliminating it as an issue, and expect that the Supremes will throw it out.
With a razor thin majority in congress, this may be the best we can do. But Bush's die-hards would forgive him for signing McCain-Feingold, knowing it was a manuever. They may not forgive him signing a weapons ban, and bolt. You and I might stick with him, but enough will bolt to hand the election to the Dems. It is a risky gambit. It must die in committee or get ready for a Liebermann presidency.
I like Liebermann. Think he would make a great ex-senator. Don't want to think about a Liebermann Administration.
If there is any additional garbage added to the AWB and it somehow makes it to Bush's desk, he'll be able to sign it without breaking any promises whatsoever. It might not be a bad idea to convince someone like McCain to add something extra in there for that very reason [plus it would aid in the 'unelect John McCain' efforts].
If the thing does get out of Congress, things will be difficult, but that would be so whether or not Bush signs it, since whatever Republicans went along with it would have drawn bullseyes on their backs come election time.