Brief Summary
The Set-Up
Joe McCarthy had been heading for a showdown with the Army for quite some time. Angry about his failure to get any dirt on an alleged spy ring at the Monmouth, NJ Army base, he accused the Army of being "soft on Communism" and trained his guns on the Army Secretary in televised hearings starting on April 22, 1954. The Army decided to counter with allegations that McCarthy's aide Roy Cohn had tried to interfere with the military by demanding special consideration for his friend G. David Schine, another McCarthy aide, who was about to be drafted.
Long story short: total rom com.
The Text
The first section is about exactly what Roy Cohn said when he attempted to get special treatment for David Schine. Essentially, Cohn didn't want his pal stationed overseas when a cushy commission in New York was so much more convenient. The testimony alleges that Cohn was abusive and threatening in his demands about Schine—he'd "wreck the Army." That's so Roy.
While the confrontation between Welch and McCarthy is what's famous, McCarthy wasn't the one on the stand here. Cohn was the guy being interrogated. McCarthy was objecting to Welch's questioning, which was intentionally ridiculing the senator's methods. Welch was sarcastically demanding to know how many Communists were in specific places, so they could waste no time in getting rid of them.
McCarthy then stepped in to bash Fred Fisher, a young attorney in Welch's firm, whom he accused of belonging to a Communist organization and wanting to spy on McCarthy's subcommittee investigations. That's when Welch got serious. He dropped the sarcasm with Cohn and confronted the senator for his cruel, reckless tactics. To McCarthy's shock, people cheered. McCarthy attempted to regain the upper hand, but it didn't work. At all.
TL;DR
Frustrated by Welch's ridiculing of Roy Cohn, McCarthy attempted a baseless smear on a young guy who worked in Welch's office…and McCarthy got schooled—hardcore.