Yeah, it's called baiting the voter. All politicians do it; tweaking their message to special interest groups they want to vote for them.
The bigger mandate though is to work for the good of the nation; it DOES override promises to special interests. Even if Obama wanted to keep his promise to the Armenian diaspora then his sense of duty should forbid him to do it if that means harming the interests of the republic his has sworn (not just promised) to protect.
I think it's nonsense to talk about broken promises by politicians if keeping their promise means breaking the only real commitment that they signed up to.