The two were arrested late last month and are being held in federal custody without bond. Their arrests were made public on Oct. 27. No trial date has been set.
Wearing black-and-white striped prison uniforms and with chains around their wrists, waists and ankles, Cowart and Schlesselman spoke only to say "not guilty" during a brief hearing before a federal magistrate in Memphis. Defense and U.S. attorneys did not comment on the case.
The charges in the seven-count indictment carry a maximum punishment of 50 years in prison and fines of $540,000.
Court records say Cowart and Schlesselman, whom authorities say are white supremacist skinheads, told investigators they planned to conduct a national crime spree that would include a string of armed robberies and the murders of 88 black people.
The number has significance for white supremacists. "H" is the eighth letter of the alphabet and 88 is skinhead code for "Heil Hitler," authorities say.
The killing spree, the records say, was to culminate with a suicide attack on Obama, which Cowart and Schlesselman would launch from a speeding car while wearing top hats and white tuxedoes.
The two were arrested about 70 miles north of Memphis after an acquaintance told sheriff's deputies they had shot out a window of a rural black church. After questioning Cowart and Schlesselman, local authorities notified federal investigators.