Well, this is why I would never ever date someone who disagreed with me on fundamental issues like religion & politics, because it would lead to arguments & a possible break up between the two of us. You can't avoid talking about things like religion, & politics in this case, as both shape a person's worldview.
I think that as hard as it may be, if you & your girlfriend really can't agree on your political stance, then you should maybe break up. The reason I say this is because it is not right for you to forcibly surrender your support for Donald Trump just because your girlfriend does not like his political beliefs, & it is not right for your girlfriend to even ask or expect such a thing from you.
I advise you in the future to only date people, like I would, who share the same stance with you on fundamental issues such as religion, politics, etc, otherwise it could lead to a break up.
Whether you break up or not, I hope that you get through it all.