Davis himself pleaded to the authorities to move his case to trial on more than one occasion.
The authorities were fearful that should a trial for treason be commenced the outcome could not be controlled and would likely be an embarrassment to the republic for the testimony that would have become public regarding the execution of the war by the administration.
Should Davis be found not guilty by reason that secession was not unconstitutional, could you imagine the outcome? Civil unrest and another insurrection by the people for the current administration to put down. The army may not have been willing to use the tactics necessary for shutting down the peoples' voice. The populace would have been so enraged at the prospect of being misled by the Lincoln regime for the deaths of 620,000+ Americans, untold misery, and an enormous financial expenditure that a tremendous backlash might have commenced thereby threatening the very lives of those in power that were responsible for the prosecution of the war.
No one in the government was prepared to take that chance, ergo no trial!
Yep.
Considering one of the judges who would have tried the case, John Underwood, was a die-hard Union supporter and the other judge who would have tried the case, Chief Justice Salmon P. Chase, would later write the majority opinion in the Texas v. White decision ruling the Southern acts of unilateral secession unconstitutional, I believe the chances of a Davis trial being dismissed on the those grounds hovered between zilch point squat and none. Also, the Davis trial would have been a criminal trial. Criminal trials do not decide what is Constituional and what is not. Only the Supreme Court can do that.
Since the trial would have been held in Virginia there was a very real fear that some people on the jury would not have voted guilty under any circumstances. But I believe that a jury could have been found who would have convicted. Jury packing is not a 21st Century discovery.