Why does blind faith in a political affiliation over-rule rationality and common sense?

as one ages we see the general trends of political parties in and out of power. The two major parties in the US both suck but one is generally less awful than the other for most of us. I will always vote a straight party line and nothing the other party has to say means anything to me because, in over fifty years of watching them and listening to them I know they are pathological liars.