I was just reading on McCarthy on Wiki and came across this:

In what played out to be the most dramatic exchange of the hearings, McCarthy responded to aggressive questioning from Army counsel Joseph Welch. On June 9, 1954, day 30 of the hearings, Welch challenged Cohn to give McCarthy’s list of 130 subversives in defense plants to the office of the FBI and the Department of Defense “before the sun goes down”.[24] In response to Welch’s challenge, McCarthy suggested that Welch should check on Fred Fisher, a young lawyer in Welch’s own Boston law firm whom Welch planned to have on his staff for the hearings. McCarthy then mentioned that Fisher had once belonged to the National Lawyers Guild (NLG), a group which Attorney General Brownell had called “the legal bulwark of the Communist Party”.

Welch revealed he had confirmed Fisher’s former membership in the National Lawyers’ Guild approximately six weeks before the hearings started.[27] After Fisher admitted his membership in the National Lawyers’ Guild, Welch decided to send Fisher back to Boston. His replacement by another colleague on Welch’s staff was also covered by The New York Times. Welch then reprimanded McCarthy for his needless attack on Fisher, saying that “Until this moment, Senator, I think I never really gauged your cruelty or your recklessness.” McCarthy, accusing Welch of filibustering the hearing and baiting Cohn, dismissed Welch’s dissertation and casually resumed his attack on Fisher, at which point Welch angrily cut him short:

“Senator, may we not drop this? We know he belonged to the Lawyer’s Guild… Let us not assassinate this lad further, Senator; you’ve done enough. Have you no sense of decency, sir? At long last, have you left no sense of decency?”

Welch excluded himself from the remainder of the hearings with a parting shot to McCarthy: “You have brought it out [the Fisher/NLG affair]. If there is a God in heaven, it will do neither you nor your cause any good!” After Welch deferred to Chairman Mundt to call the next witness, the gallery burst into applause.

Fisher was relatively unscathed by the incident and went on to become a partner in Boston’s prestigious Hale & Dorr law firm and organized its commercial law department. He also served as president of the Massachusetts Bar Association and as chairman of many committees of the American and Boston bar associations. He was a former trustee of the National Institute of Trial Advocacy and chairman of the Franklin N. Flaschner Foundation in Waban, Mass., while Welch’s maneuvering helped to ruin McCarthy’s life and career. McCarthy died at the relatively young age of 48.
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After hearing 32 witnesses and two million words of testimony, the committee concluded that McCarthy himself had not exercised any improper influence on behalf of David Schine, but that Roy Cohn, McCarthy’s chief counsel, had engaged in some “unduly persistent or aggressive efforts” on behalf of Schine. The conclusion of the committee also reported questionable behavior on the part of the Army: That Secretary Stevens and Army Counsel John Adams “made efforts to terminate or influence the investigation and hearings at Fort Monmouth”, and that Adams “made vigorous and diligent efforts” to block subpoenas for members of the Army Loyalty and Screening Board “by means of personal appeal to certain members of the [McCarthy] committee”. Before the official reports were released Cohn had resigned as McCarthy’s chief counsel, and Senator Ralph Flanders (R, Vermont) had introduced a resolution of censure against McCarthy in the Senate.

Despite McCarthy’s acquittal of wrongdoing in the Schine matter, the Army–McCarthy hearings ultimately became the main catalyst in McCarthy’s downfall from political power.

Remember, this all happened a year after the Korean War, the year after Stalin died, and only a few years before the Great Leap Forward.

McCarthy is hunting possible traitorous supporters of mass-murdering communist regimes in the Army. An investigation is found in which the army is found to have committed questionable behaviour in stymieing these investigations, while McCarthy is found to be free of any wrong-doing.

During the trial, McCarthy calls out a lawyer who was a part of a known communist organization and McCarthy is painted as the bad guy. McCarthy ends up losing his career over this trial; the communist later ends up as President of the Massachusetts Bar Association and has major roles in the organizations for training new lawyers.

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Also interesting: Fisher was a part of the Signal Corps in WW2 and the whole hearing was about McCarthy investigating the Signal Corps.