Hiring managers come in all political stripes and some would be favorably impressed, some would be unfavorably impressed and others wouldn't care either way, but just be happy with whatever actual accomplishments you made as a developer during the internship. How many people are affected depends on how negatively the organization is perceived by the general public. More would be be upset that you worked for the American Nazi party (or Black Lives Matter) than for the Republican party or some organization like Act Blue.
What you need to decide is how much you care about working for someone who would find it appalling that you did this type of work. It is difficult to hide your personal feelings on things all day long as someone of the opposite views makes it clear that he is only interested in people who agree with him. This tends to carry over to things besides politics as well as a judgemental personality type is very difficult to work for.
Personally I find this sort of thing tends to filter out the places I would not want to work in anyway. A reasonable private company to work for is going to have people of a broad variety of political opinions and hiring decisions are not made by political party (unless of course it is a political organization) or other irrelevant factors.
And of course, you may end up staying in the political sector. There are good jobs there too and the work is often interesting. If you find you like it, then the internship is an advantage.
