"Thus, Davis still faced a charge of treason. At court in Richmond, Chief Justice Chase finally joined Judge Underwood on the bench. In the mean time, the Fourteenth Amendment to the Constitution had been ratified by the states and had gone into effect on July 28. Its third section stipulated taht no person could hold office who had sworn an oath to uphold the Constitution and subsequently had participated in the rebellion. To Chase this provision offered a way around the morass of a Davis trial because there could be no double jeopardy. In conversation with George Shea, Chase made clear his viewpoint.
"Chase's opinion dictated the strategy of the Davis defense. Davis's lawyers readily admitted that in 1845 he had taken an oath to support the Constitution. They submitted a motion asking that they indictment be quashed on the grounds that the 14th Amendment had already inflicted punishement on their client. The government's attorneys contested the point. The chief counsel, Richard Dana, countered that the Constitution was not criminal law...On December 5 the court handed down a divided ruling. Chase stated that he and Underwood could not agree. He accepted the arguement tendered by the defense; Underwood rejected it. Counsel for the defense requested that the facts of the disagreement be certified to the Supreme Court. Chase so ordered. As the indictment remained in force, the federal attorney wanted a trial date set. Chief Justice Chase saidn the date could be announced after the completion of the upcoming Supreme Court term.
"William Evarts, who had become U.S. attorney general in July 1868, decided the government would push no further." -- "Jefferson Davis, American" by William J. Cooper, Jr. pp 581-582
Looks like Davis' attorneys jumped at the chance to avoid a trial.
Three years had passed. Rewards had been paid for the arrest of Davis and other Confederate officials. NONE was EVER tried. ALL were released without trial. The government clearly NEVER pushed at all for a real trial in a real court. The only thing the government clearly pushed for was an eternal continuance.
Varina Davis, Jefferson Davis, A Memoir, 1890, Vol 2, p. 777
The Chief Justice, the Attorney-General, and the Secretary of War were opposed to an early trial. Many efforts were then made with President Johnson to procure the pardon of Mr. Davis. He said, he made it an inflexible rule, "never to grant a pardon on petition, unless it was accompanied by an application from the individual seeking the executive clemency." Mr. Davis, on the other hand, always said, "to ask for pardon was a confession of guilt," and that such an application would prejudice his case.
Davis never applied for the pardon and Johnson waived his "inflexible rule."
The attorneys favored accepting Chase's creative reasoning regarding the 14th Amendment because its scope would have applied universally to all remaining Confederate officers and function in a manner similar to the unconditional pardon that Johnson issued.