Answer by taking a quote from the following article:

Joseph Raymond McCarthy (November 14, 1908 - May 2, 1957) was an American politician who served as U.S. Senator from the state of Wisconsin from 1947 until his death in 1957. Beginning in 1950, McCarthy became the most visible public face of a period in the United States in which Cold War tensions fueled fears of widespread Communist subversion. He is known for alleging that numerous Communists and Soviet spies and sympathizers had infiltrated the United States federal government, universities, film industry, and elsewhere. Ultimately, the smear tactics that he used led him to be censured by the U.S. Senate.

One of the strongest bases of anti-Communist sentiment in the United States was the Catholic community, which constituted over 20% of the national vote. McCarthy identified himself as Catholic, and although the great majority of Catholics were Democrats, as his fame as a leading anti-Communist grew, he became popular in Catholic communities across the country, with strong support from many leading Catholics, diocesan newspapers, and Catholic journals. At the same time, some Catholics did oppose McCarthy, notably the anti-Communist author Father John Francis Cronin and the influential journal Commonweal. McCarthy established a bond with the powerful Kennedy family, which had high visibility among Catholics. McCarthy became a close friend of Joseph P. Kennedy Sr., himself a fervent anti-Communist, and was a frequent guest at the Kennedy compound in Hyannis Port. He dated two of Kennedy's daughters, Patricia and Eunice. It has been stated that McCarthy was godfather to Robert F. Kennedy's first child, Kathleen Kennedy. This claim has been acknowledged by Robert's wife and Kathleen's mother Ethel, though Kathleen later claimed that she looked at her christening certificate and that her actual godfather was Manhattanville College of the Sacred Heart professor Daniel Walsh. Robert Kennedy was chosen by McCarthy as a counsel for his investigatory committee, but resigned after six months due to disagreements with McCarthy and Committee Counsel Roy Marcus Cohn. Joseph Kennedy had a national network of contacts and became a vocal supporter, building McCarthy's popularity among Catholics and making sizable contributions to McCarthy's campaigns. The Kennedy patriarch hoped that one of his sons would be president. Mindful of the anti-Catholic prejudice Al Smith faced during his 1928 campaign for that office, Joseph Kennedy supported McCarthy as a national Catholic politician who might pave the way for a younger Kennedy's presidential candidacy. Unlike many Democrats, John F. Kennedy, who served in the Senate with McCarthy from 1953 until the latter's death in 1957, never attacked McCarthy. McCarthy had refused to campaign for Kennedy's 1952 opponent, Republican incumbent Henry Cabot Lodge Jr., due to his friendship with the Kennedys. When a speaker at a February 1952 final club dinner stated that he was glad McCarthy had not attended Harvard College, an angry Kennedy jumped up, denounced the speaker, and left the event. Asked by Arthur M. Schlesinger Jr. why he avoided criticism of McCarthy, Kennedy said, "Hell, half my voters in Massachusetts look on McCarthy as a hero." CANNOTANSWER

What their involvements entailed?

He dated two of Kennedy's daughters, Patricia and Eunice. It has been stated that McCarthy was godfather to Robert F. Kennedy's first child,