Originally Published: 11 APR 23 05:01 ET

Updated: 11 APR 23 10:30 ET

By Kevin Liptak, CNN

(CNN) -- When President Joe Biden was isolating with Covid in the White House last summer, atop the stack of books on his desk was a 320-page paperback: "JFK in Ireland."

The last Irish Catholic president visited his ancestral homeland in 1963, five months before his assassination. He told his aides afterwards it was the "best four days of my life."

Sixty years later, the current Irish Catholic president (Secret Service codename: Celtic) departs Tuesday for his own visit bound to make a similar impression -- first to Northern Ireland, which is part of the United Kingdom, and then onto Ireland from Wednesday through Saturday.

Part homecoming, part statecraft and part politics, this week's trip amounts to a timely intersection of Biden's deeply felt personal history with his ingrained view of American foreign policy as a force for enduring good.

Departing Washington on Tuesday, Biden described his goal as "making sure the Irish accords and the Windsor Agreement stay in place -- keep the peace."

"Keep your fingers crossed," he told reporters before boarding Air Force One.

The visit is timed to commemorate the 1998 signing of the Good Friday Agreement, which ended decades of sectarian bloodshed in Northern Ireland known as The Troubles. The agreement came about with significant American investment, particularly from Democrats like Bill Clinton and Sen. George Mitchell, a legacy Biden is eager to highlight when he stops in Belfast starting Tuesday.

But it will be his personal engagements in the Republic of Ireland later in the week, including stops in County Louth and County Mayo to explore his family roots, that will best capture what Biden himself has described as perhaps his single most defining trait.

"As many of you know, I, like all of you, take pride in my Irish ancestry," he said during a St. Patrick's Day luncheon last month. "And as long as I can remember, it's been sort of part of my soul."

Described by Ireland's prime minister last month as "unmistakably a son of Ireland," Biden has at various moments ascribed his temper, his nostalgic streak, his politics and his humor all to his Irish roots. He quotes poets like William Butler Yeats and Seamus Heaney freely; the most famous passage from Yeats' "Easter 1916" has appeared no fewer than 12 times in Biden's public remarks since he took office.

"They think I do it because I'm Irish," Biden said recently. "I do it because they're the best poets."

Biden's last visit coincided with Brexit vote

Ahead of the trip, the White House distributed an extensive family genealogy stretching as far back as 1803, to the shoemakers and civil engineers and union overseers who would eventually leave Ireland on ships bound for America. Most left during the Irish famine of the 1840s and 1850s on what Biden has called the "coffin ships" because so many of their passengers didn't survive the passage.

His ancestors' experiences have left indelible impressions on Biden, whose persona is defined by eternal optimism despite his own experience of profound loss.

"One of my colleagues in the Senate, Daniel Patrick Moynihan, once made this simple but profound observation about us Irish: 'To fail to understand that life is going to knock you down is to fail to understand the Irishness of life,'" he wrote in his 2017 memoir.

Returning to Ireland as president has long been in the cards for Biden, who is also planning to meet with Irish leaders, address Parliament and deliver a nighttime speech in front of St. Muredach's Cathedral, in the northwest of Ireland, before returning to Washington on Saturday. The White House said Biden's great-great-great grandfather Edward Blewitt sold 28,000 bricks to the cathedral in 1828 to construct its pillars.

He'll be joined members of his family for the journey, including his son Hunter and sister Valerie. When he visited as vice president in 2016, he spent six days crisscrossing the island with several grandchildren and his sister, a newly generated family-tree in hand.

By coincidence, Biden was on that visit to Ireland the same day a majority of British voters elected to leave the European Union, a decision he opposed and which posed thorny questions for Northern Ireland, which is part of the UK.

As aides set to work planning his visit as president, Brexit's legacy continued to loom. A dispute over trade rules between the UK and the European Union, to which the Republic of Ireland belongs, tested the Good Friday agreement and its fragile peace.

It was a matter Biden took outsized interest in upon taking office. He warned successive British prime ministers to resolve the dispute before the anniversary -- tacitly hinging his entire trip on it. After months of negotiations, the current PM Rishi Sunak struck a deal resolving the dispute in February, though Northern Ireland's main unionist political party has yet to sign on. Still, the arrangement paved the way for Biden's visit this month.

Sunak is expected to meet Biden when he arrives, and the two will meet for talks in Belfast on Wednesday.

Biden hopes to use his trip as a reminder of what sustained diplomacy can yield at a moment America's role abroad is being debated. An isolationist strain among Republicans has led to questions about the durability of Washington's global leadership. The Good Friday Agreement, brokered by the United States, stands as one of the most lasting examples of US diplomacy from the end of the 20th century.

"President Biden has been talking about liberal internationalism as something that can return, he talks about democracy versus autocracy, all of this kind of stuff. So within that, I think that he wants to see good examples of the rule of law in US foreign policy. And this is a great example of that. This was an achievement," said Liam Kennedy, director of the Clinton Institute for American Studies at the University College Dublin.

"The Good Friday Agreement is certainly one of those things where you can get real bipartisan buy-in in Washington," Kennedy said. "Believe me, that's a pretty unusual thing."

America's role in Good Friday Agreement

The bloody tensions between Protestant Unionists, who support remaining part of the United Kingdom, and Catholic Irish Nationalists, who support reunification with the Republic, have mostly been left in another era. The Troubles led to more than 3,500 deaths, most of them civilians, and even more casualties.

As a senator, Biden was outspoken in favor of American peacemaking efforts in Northern Ireland. He also opposed extraditing IRA suspects from the US to Britain, arguing the justice system that existed in Northern Ireland at the time wasn't fair.

In 1988, he told the Irish America magazine in a cover story (headline: "Fiery Joe Biden: White House bound?") that as president he'd be active in trying to reach a peace.

"If we have a moral obligation in other parts of the world, why in God's name don't we have a moral obligation to Ireland? It's part of our blood. It's the blood of my blood, bone of my bone," he said.

A decade later, three-way talks between the US, Ireland and Britain yielded the Good Friday Agreement, which sought to end the bloodshed through a power sharing government between the unionists and nationalists.

Yet that government has functioned only sporadically in the quarter-century since the accord was signed and has been frozen for more than a year after the Democratic Unionists withdrew because of the Brexit trade dispute.

John Finucane, a member of the British Parliament from Irish nationalist Sinn Fein party, said Biden's visit to Northern Ireland this week would be a "huge help" toward resolving some of the lingering differences.

A lawyer whose own father was murdered by Loyalist paramilitaries in collusion with UK state forces in 1989, Finucane said Biden's visit was a reminder of the American role in brokering peace.

"It's no secret that I don't think we would have had a peace process or certainly a Good Friday Agreement without the involvement of the American administration, and successive American administrations in implementing our peace," he said. "Joe Biden himself has a very strong track record in supporting our peace process. So I think it is very fitting that he will be coming here next week."

Still, the threat of violence has never entirely disappeared, a reality made evident when British intelligence services raised the terrorism threat level in Northern Ireland from "substantial" to "severe" in late March.

An operation called "Operation Rondoletto" taking place over Easter weekend ahead of Biden's visit was set to cost around $8.7 million (£7 million), the police service said, and include motorcycle escort officers, firearms specialists and search specialists.

Asked last month whether the heightened terror level would dissuade him from visiting, however, Biden hardly sounded concerned.

"No, they can't keep me out," he said.

This story has been updated with additional developments.