Eh.. it's messy isn't it. Politically motivated libertarians strongly support both 2nd amendment and oppose back doors. Generally speaking, the govt is always seen as the biggest threat to guard against.

Probabaly the ones supportive of backdoors are as you said, simply "trusting" of the current leader they voted for but would immediately oppose the same policy coming from a Democrat.

...which is the exact impulse and logic that should push all partisans to distrust government power to snoop on communications. There will always be someone in charge somewhere that you don't trust.