You might be, if your single issue was global warming. (Sorry!
Climate Change.
)
If it's 2A though, that is the best litmus test for freedom that you can have. There is no way to know what a politician truly thinks or says, but if you look at his record, and look at his stance on guns in the hands of the people, that will tell you if he will take or protect your freedom.
Everything else is anciliary to protecting liberty.
I'd say you'd be crazy
not to be a 2A single issue voter.