On this matter, Ireland is something of an outlier in Europe. In a January poll, 71 percent of respondents in Ireland said they believed Palestinians lived under an Israeli apartheid system; in another poll in February, 79 percent said they believed Israel was committing genocide. By contrast, no more than 27 percent of people in seven Western European countries said they sympathized more with Palestinians than with Israelis. Here in Britain’s first colony — a status cast off through a war of independence — empathy for Palestinians is deeply rooted, born of shared historical experience.

This feeling has given rise to an extraordinary wave of pro-Palestinian actions in Ireland since the war began. The array of protests — countless concerts, fund-raisers and demonstrations calling for a cease-fire and an end to the bombardment of Gaza — goes far beyond any fringe concern. Protests in Ireland are large and spread across the country, with attendees diverse in age, class, ethnicity and political affiliation. They bring together trade unionists, Gaelic football players, journalists, ordinary citizens young and old, politicians, health care workers, L.G.B.T.Q. people and many more. It is a truly national phenomenon.

Around the world, chants at pro-Palestinian demonstrations are pretty similar. But over the winter, a specific chant took hold on Irish streets. Though St. Patrick’s Day was months away, protesters looked to the annual meeting in Washington between the Irish prime minister, or taoiseach, and the American president. At the Oval Office every March 17, the Irish leader presents to the American president a bowl of shamrock. The chant, taking notice of this tradition, was bracingly simple: “No shamrocks for Genocide Joe.”

It caught on, becoming the aural centerpiece of protests across the country, especially at the largest demonstrations on Saturdays in Dublin’s city center. It was transformed with a slight modification into a mural in Belfast, a city where Palestinian flags have long flown in nationalist communities; was spray-painted along tram tracks in Dublin; and took hold on social media, where people drew black shamrocks on the palms of their hands. Such agitation coalesced around the demand that the prime minister, Leo Varadkar, boycott this year’s White House visit.

Along with that demand, Mr. Biden became the focus of Irish ire. At protests he was rebuked by public figures, not least Bernadette Devlin McAliskey, a hero of the 1960s civil rights movement in the north of Ireland. In the press, commentators lined up to pass judgment on the American president, including the acclaimed novelist Sally Rooney, who characterized the assault on Gaza as “Biden’s war.” The criticism, at times, has been intimate. In County Louth, where Mr. Biden’s great-grandfather James Finnegan was born, a group of people gathered at a graveyard to castigate the president for betraying his roots.