In response to my accusation that President Buchanan subverted justice in a murder trial, ai denies it. Buchanan was a democrat, so that tracks. I heard the story on an episode of The Fat Electrician.

There is no historical evidence that President James Buchanan subverted justice in a murder trial.
However, the most famous historical instance of President Buchanan interfering with the judicial system occurred during a highly consequential civil rights and constitutional case, rather than a murder trial:

The Dred Scott Decision (1857): Prior to his inauguration, Buchanan explicitly pressured Northern Supreme Court Justice Robert Cooper Grier to vote with the Southern majority in the Dred Scott v. Sandford case. He wanted a sweeping decision that would declare Congress had no power to restrict slavery in U.S. territories. Buchanan then lied in his inaugural address, claiming he would cheerfully submit to the court's decision, despite already knowing and influencing the pro-slavery outcome.

If you are thinking of a different "Buchanan" ...