Shake off the legalese and most bank account agreements say "The bank can close your account for any reason whatsoever, or even no reason at all, any time we feel like it." Unless you negotiate different terms or the bank is closing the accoumt for an illegal reason (like your race, sex or some handicap) you're pretty much screwed.
It would be interesting for the NRA to open a bank, but I’m sure Obama would work to shut them down.