4. Republicans will be fine with an AWB because it doesn't actually do anything
In fact, I'd imagine Republicans would absolutely love to have an assault weapons ban pass soon.
1) It lets their few remaining moderates say "see, I voted for bipartisan gun control legislation"
2) It lets them rile up gun owners who know what it does and see it as a pointless culture war "fuck you" to them
3) It doesn't affect, for instance, the gun the shooter in Newtown used, so no actual access to firearms are lost
If I were a Republican I'd be all for this. If it goes down like in 1994, people (hell, even some legislators) will think that it's banning semi-automatic rifles with detachable magazines (which is what is actually important if you're trying to stop mass shootings), gun makers will remove the bayonet lugs from their rifles and sell them legally (at sky-high prices to the rubes), and gun control as an issue will be dead for another two decades.