On what grounds should such talk have been taken before the court? Courts rule on actions taken, not contemplated or talked about.
When Jefferson Davis gave his farewell speech to the U.S. Senate, he began by saying, "I rise, Mr. President [John C. Breckinridge], for the purpose of announcing to the Senate that I have satisfactory evidence that the State of Mississippi, by a solemn ordinance of her people in convention assembled, has declared her separation from the United States."
He then announced that since his functions were terminated, he would be going home to Mississippi. Foote writes that Davis stayed in Washington a few days afterward, hoping to be arrested for treason, thereby testing the doctrine of secession in the federal courts.
Was there not sufficient cause in Davis's announcement -- that he was resigning from the Senate to join a group of "rebels" -- to provide for a test case?
Yeah, well there's a reason James Buchanan always lands near the bottom of the presidential rankings. His only agenda was to avoid doing anything until his term was up and he could get out of town.
Which goes more towards pointing out Davis's abysmal understanding of the law and the Constitution tahn anything else. The Constitution defines treason. What exactly had Davis done that qualified? Resigning from the Senate isn't treason. Advocating secession isn't treason. The South hadn't started the war yet. What treasonous act had been committed?
Now assuming for the sake of arguement that Davis had committed treason. He would have been arrested, tried in federal court, convicted, appealed, conviction upheld, and appealed again before it would have gotten to the Supreme Court. The rebellion short-circuited that path just a little bit.