This adds a lot of complication, and in the real world, nothing is cleanly and perfectly opposite. Imagine two art museums bidding on a painting. Are they putting their money in opposite places, or are they working together to increase the amount of art displayed in public. (bidding also increases production)
Also, political donations are actually quite small, comparitively speaking. A different prisoners dilemma operates. Not saying the other effect is absent, just smaller.
A set of Democrats would each like the democrats to win, but they also want a bigger TV. They would each prefer everyone to donate, but their donation on its own won’t make a big difference, so they buy a new TV.