In Morse v. United States, the Supreme Court ruled on a case involving a man who had been convicted of violating the National Prohibition Act by possessing and selling alcohol. The defendant argued that his conviction should be overturned because he was not allowed to cross-examine one of the government's witnesses during his trial. However, the court rejected this argument, stating that while defendants have a right to confront their accusers in court under normal circumstances, there are exceptions when it can be shown that allowing such confrontation would hinder justice or endanger public safety. In this particular case, it was determined that allowing cross-examination could potentially expose undercover agents working for law enforcement agencies and put them at risk. Therefore, despite acknowledging potential issues with fairness in trials where defendants cannot fully question all witnesses against them; they upheld Morse’s conviction.

In the dissenting opinion for Morse v. United States, Justice Oliver Wendell Holmes Jr. argued that the defendants' convictions should be overturned because they were not given a fair trial due to public prejudice and hostility against them at the time of their trials. He believed that this bias had influenced both the jury's decision and the judge's conduct during proceedings, leading to an unfair outcome. Furthermore, he disagreed with majority’s interpretation of Espionage Act of 1917 under which defendants were convicted; arguing it was too broad in scope and could potentially infringe upon First Amendment rights by criminalizing criticism or opposition to government policy during wartime. Thus, according to him, there was reasonable doubt about whether defendants’ actions truly constituted crime as per Espionage Act or merely represented exercise of free speech right protected by constitution.