Sen. Marco Rubio’s (R-Fla.) associates, furious about fellow Republican Sen. David Vitter (R-La.) calling the Floridian “nuts” and “naïve” over his immigration reform efforts, are hitting Vitter where it hurts.

“David Vitter has done some nuttier things in his life,” a source close to Rubio wrote in an unsolicited email to POLITICO.

That’s a not-at-all subtle reference to Vitter’s 2007 admission that his phone number appeared on a client list of a Washington, D.C. madam. A New Orleans-based prostitute and madam have also, separately, accused Vitter of being a client, but he has denied those charges.