It's the link that dare not speak its name. For good or ill, he was one of the most influential and significant figures in US history over the past 60 years.
He turned the political system upside down, generating turmoil and mayhem with his sensational and largely unsubstantiated claims about communist subversion in government. Already a senator, if he had played his cards right he could have gone on to become vice-president and, from there, who knows?
He also had more Irish blood coursing through his veins than virtually any other leading American politician of recent decades. In the normal run of things we would be making a big fuss about the connection. Remember Ronald Reagan and Ballyporeen? Richard Nixon and Timahoe? John F. Kennedy and New Ross? Clinton and the Cassidy connection?
As one or two names on that list suggest, we have never been overly fastidious when it comes to American politicians laying claim to Irish ancestry. Sure they might garner a few extra votes and we might attract a few more tourists. Fawning over powerful American leaders is probably good for investment, so everybody's happy with the deal.
But Joseph R. McCarthy was apparently too strong even for our hardy stomachs. Never mind that his grandfather, Stephen McCarthy, was a Tipperary man who emigrated to the US the year after the Great Famine. Never mind that both parents of his mother, Bridget "Biddie" Tierney, were also born in Ireland. Never mind that he built his original political base among Irish and other immigrants in Wisconsin.
His impact was severe, but his time in politics was short and, broken by drink and political adversity, McCarthy died in 1957. However, he was back in the news again lately. Earlier this month, almost on the 46th anniversary of his death, fresh transcripts of his Senate hearings into allegations of communist subversion and espionage were released for the first time. These were private hearings where, as usual, he browbeat and bullied the witnesses, but the transcripts show that, whenever someone stood up to him, they were left alone thereafter. If a witness was clearly intimidated, that person was likely to be called for a further hearing, this time in public.
It is a flashback to one of the ugliest periods in US political history. The practice of making reckless and largely unfounded allegations came to be known as "McCarthyism". Little did young Stephen McCarthy know as he boarded the ship that day back in 1848 that his surname would eventually become part of the language.
We now know that Joe McCarthy's career ended in disgrace, that he was ultimately exposed on television for the bully that he was, and later formally censured in a vote of the US Senate. But at his height he was a terrifying figure, who maligned the reputations of many good people and ruined numerous lives.
Lately there has been an attempt to rehabilitate McCarthy. Documents released after the collapse of the Soviet Union provide compelling evidence that some US citizens were indeed involved in espionage activities on the Kremlin's behalf. But despite McCarthy's claim to be "digging out skunks", the conservative historian Paul Johnson says there is no evidence he ever unearthed any subversive not already known to the authorities. It's a good thing then, from a political viewpoint, that we don't honour the memory of Joe McCarthy and that there are no shrines and no bus tours. It is bad enough that his spirit lives on amid reports of a "new McCarthyism" in America.
We are familiar with forms of McCarthyism in this country. There was a "red scare" in Ireland during the 1950s, despite the fact that communists were about as plentiful as white blackbirds. With the onset of the Northern troubles, even those who held non-violent nationalist or republican views were regarded with suspicion. Lifelong opponents of violence like John Hume were vilified for their efforts to achieve a peace settlement. A stifling conformity was imposed that impeded efforts to end the violence and shadows of this cultural repression still remain. Sometimes the most censorious are those who flirted energetically in the past with violent people and organisations.
But McCarthyism, whether of the Irish or US variety, could not have flourished without the ready-made excuse provided, on the local scene, by the terrible deeds of the Provisional IRA and, in a broader context, by the proliferation of totalitarian regimes in eastern Europe and Asia.
McCarthyism was a reactionary, negative and utterly regrettable phenomenon but its excesses were minor compared to what was happening simultaneously in the communist bloc. During the years that McCarthy was at his height, 1950-54, the former Czechoslovakia was in the grip of a Stalinist terror that led to the imprisonment or execution of about a quarter of a million dissidents, to say nothing of what was happening in other Soviet satellites.
Strangely, we don't hear a lot about this element of the equation when McCarthyism is being assessed. "Uncle Joe" Stalin was a greater enemy of liberty than "Tailgunner Joe" McCarthy, although as far as I'm aware his grandmother didn't come from Ireland.