Earlier quoted context omitted.
Explain how this works. A blue party voter writes to another blue party voter: Hey, let's vote blue this year. NSA that intercepts the message and __________.
The thing being suggested here is that the campaign of the incumbent is reading all the communications of the campaign of the challenger. I don't think anything of the sort actually happens or is really that easy to (completely secretly!) make happen, but that's the proposed scenario.
My kids tested sending https://kamalaharris.info and https://joebiden.info to each other on Instagram, in private messages. The sender would see that the message was successfully sent, but it would never arrive.
Another case is that the person who ran the primary campaign for Kamala Harris now works at Twitter, where he blocked an opponent's campaign account.