Developing my spike??

It sounds like you have been developing your spike! It would really stand out to me that you are another STEM applicant, but one with political aspirations and political ECs. It could help you to do some research into people who chose a similar path and the decisions they have made. Even if it's just reading articles or academic papers written by people who chose a similar path- you may find yourself attracted to the amount of quantitative data cited or notice a creative problem-solving approach. Exposing yourself to this really helps build a lexicon to communicate why you are choosing this path.

For example, I watch the show Crossfire, a political debate show on CNN. One of the co-hosts, John Sununu, is the former Governor of New Hampshire and was White House Chief of Staff under President George H.W. Bush. He also has three degrees in Mechanical Engineering. I can definitely see his STEM roots in how he debates. His son is the current Governor of New Hampshire. But that's not the only way his son followed in the father's footsteps: He graduated from MIT with a bachelor's degree in civil and environmental engineering. There are so many people who make up politics. There's definitely room for STEM majors.

Signed,

Someone similarly drawn to a major many find incongruent with my career aspirations

I suppose it will depend on the school but in general (in the US anyway) you are technically applying to a school not a major. I don't think showing a breadth of interests is going to hurt you. After all, responsibility and leadership are desirable traits in all students not just political science majors. If you are worried about it, you could use your essay to explain how your interests connect.

Don't feel like you have to have a spike! Try tapping into what you have learned from those STEM related classes and political/leadership, and using those for your essays!!! I'm in a similar boat, so I totally feel you! Freewriting helped me a lot. You got it!