Political campaign contributions

Politically engaged readers in the US who contribute financially: How do you decide which election campaigns to give money to? I’m getting about a dozen requests a day and I’m so sick of them I’m disinclined to support any, but that doesn’t feel wise. I believe in supporting my representatives but it also seems like a good idea to support key races elsewhere but I don’t know how to decide which ones. I’d rather pick a few to focus on than give small amounts to all of them.