Because they see the republican party as the “christian” party...and they aren’t christians.
It is not surprising that they see the Republican Party as the Christian Party. That's how the party sees itself. The local party here, in particular, is very sectarian.
It’s amazing the number of liberal Jews I know who are utterly convinced that if some evangelic Republican gets power, he/she Republican will start conducting pogroms!
Also there will be forced “Christianization” of Jewish kids in school as well as other utterly irrational statements.
I remember one time bursting out laughing when I heard one say this with complete seriousness.
This nuttiness is almost like ‘Articles of Faith’ with them.