The letter, which the McDaniel campaign first released on Wednesday and has been sending out to supporters on Thursday, refers to criticism by the Cochran campaign toward McDaniel in response to pro-McDaniel blogger Clayton Thomas Kelly being arrested for photographing Cochran's bedridden wife at her nursing home for an anti-Cochran video.
"Over the past several weeks, your campaign has resorted to shameful slander, even going so far as to call me a 'criminal' without a shred of evidence to back up these accusations," McDaniel also said in the open letter.
"No doubt, many political campaigns resort to juvenile behavior when they are down in the polls, but this kind of slander goes beyond childish pranks. It is, frankly, an embarrassment to our great state. Mississippi deserves better than this."
McDaniel also repeated his call for a debate with Cochran.
"Many television stations across Mississippi have extended debate invitations to our campaigns and I remain more than willing to participate in any of the debates we've both been asked to join," McDaniel wrote. "To date, you have refused to come home to Mississippi and debate."