Effect:

"It seems like every other week some association calls looking for donations."

Cause:

"So far this year I've already donated to my local Police Officers Association ($100) and my local Legion Post ($25)[...]"

You are now on their list someplace, and I wouldn't put it past them passing that list around. The more you give the more they are going to hit you up for more. If you do give, do it anonymously is my advice.