The man, a retired public relations professional in the western United States who asked not to be identified, read ProPublica’s story this week on Kasowitz and sent the lawyer an email with the subject line: “Resign Now.’’

Kasowitz replied with series of angry messages sent between 9:30 p.m. and 10 p.m. Eastern time. One read: “I’m on you now. You are fucking with me now Let’s see who you are Watch your back , bitch.”

In another email, Kasowitz wrote: “Call me. Don’t be afraid, you piece of shit. Stand up. If you don’t call, you’re just afraid.” And later: “I already know where you live, I’m on you. You might as well call me. You will see me. I promise. Bro.”