People who only message you before a vote or a fundraiser aren’t checking in. They’re campaigning.

Contact that arrives on a schedule tied to what somebody needs is not really contact. The warmth is real enough while it lasts, and then it stops the day after the vote. The pattern is easy to see once you look at the timing rather than the tone. You are a number on a list, phrased kindly.

Look back at when the last few messages from somebody arrived and what was happening that week. You do not have to call it out or refuse to help. Just stop reading it as friendship, and spend your own effort where it is returned at random times for no reason.