Take a look at this sentence from an article in the New Yorker: “A couple of weeks after that, a woman in California called the police on three black women whom she thought were behaving suspiciously.”
No, no, no! “Who she thought were behaving suspiciously.” Here’s how you know: substitute he for who, him for whom. (If that sounds like the song “Tea for Two,” I’m right there with you.)
So: “She thought he was behaving suspiciously” “She thought who was behaving suspiciously.” And: “who she thought was behaving suspiciously.”
The New Yorker is meticulously edited. Their writers are the best of the best. If even they can’t figure out how to use whom correctly, I’d say it’s time to let it go.
Whom doesn’t add any clarity to a sentence. It confuses even excellent writers. Begone!