James Everett Dutschke was scheduled for the hearing in US District Court in Mississippi, according to court documents.
Dutschke, 42, previously pleaded not guilty and denied sending the letters.
He has been jailed since April on charges of sending ricin-tainted letters to Obama, US Sen Roger Wicker and a Mississippi judge. The judge was the only one to receive a letter, though she was not harmed. The letters to Obama and Wicker were intercepted.
Authorities first arrested Paul Kevin Curtis for allegedly sending the letters, which contained statements Curtis had often used on his Facebook page. But charges against Curtis were dropped when the investigation shifted to Dutschke. Curtis says the men have feuded for years.