In all US states except for 2, the popular vote determines who ALL the electors are from that state, so the gerrymandering does NOT have a direct impact on the result of the presidential election, or at least not very much (I believe gerrymandering can affect Maine and Nebraska electoral votes, but only a small number of them, much less than the 10% you suggest would be needed).
Gerrymandering DOES impact things like voter ID laws and other policies that can make it harder for certain people to vote, so in that way you could argue that gerrymandering indirectly affects the presidential election.
If you really want to argue that the presidential elections in the US are rigged, you should focus on voting machines I would say. But even then I think it’s a stretch.
If I were in your shoes, I would probably mention the change in tone/word choice to the lead on the project since you have a good relationship with them. Just mentioning that you noticed the change and aren’t sure about it doesn’t need to be combative, and I would be truly shocked if it cost you the job. Depending on your state it might even be illegal to fire you for something like that.
I personally would not take a stand or refuse to do the voiceover or anything like that. I would make it clear that I would do the voiceover using the script as it is written. I would think of it as providing feedback rather than making demands, which seems like it would be within the purview of a QA reviewer.
This way you can at the very least get more information about the situation - find out whether this was an intentional change. If so, it may be time to start making moves so you can eventually drop this company.