I also wonder how an assassination plot is supposed to derail this law. Because if Obama is killed, Biden takes over. After Biden, Pelosi takes over. then Harry Reid. I'm pretty sure all of those guys are pretty much in favor of the bill. How many cabinet members would they have to take out? Forgetting, of course, the logistical difficulties of assassinating this many high profile politicians surrounded by scads of security.
Also, the first assassination massively swings the pendulum of public opinion against these weird fringe reactionaries.