President Biden highlighted the strength of the ties between Ireland and the U.S. in a speech before the Irish Parliament on Thursday after his meeting with Irish President Michael Higgins in Dublin. The trip has afforded Mr. Biden the opportunity to combine diplomacy with a little exploration of his Irish ancestry.

"Today, you are amongst friends, because you are one of us," said Ceann Comhairle Seán Ó Fearghaíl, effectively the speaker of the lower chamber, addressing Mr. Biden before his speech.  

The president also spoke of the mutual and international benefit of the relationship between the two countries, "a partnership for the ages."

"The journeys of our ancestors expanded our horizons, and literally excited our imaginations," Mr. Biden said. "They became the untiring backbone of America's progress as a nation, even as they endured discrimination and were denied opportunity." 

Mr. Biden said that perhaps more than most, "the United States was shaped by Ireland." The U.S. president spoke of how Benjamin Franklin once visited the Irish parliament and said Ireland was "disposed to be friends" of America. 

"We're nations that know what it means to persevere for freedom, to brave a civil war, to toil in the vineyards of democracy," Mr. Biden said. 

That fight for democracy continues, Mr. Biden said, in turning to the subject of Russia's war on Ukraine.

"Today, Ireland and the United States are standing together to oppose Russia's brutal aggression and support the brave people of Ukraine," Mr. Biden said, prompting intense applause from the members of parliament. "President Kennedy said 60 years ago, and I quote, 'Ireland pursues an independent course in foreign policy. But it is not neutral between liberty and tyranny. And never will be.' Thank you for that. Over the past year, Ireland has proved him right."

The president's visit to the Republic of Ireland followed his trip to Northern Ireland, which is part of the U.K., to mark 25 years since the signing of the Good Friday agreement, a breakthrough that put an end to decades of violence.

On Thursday, Mr. Biden signed the guestbook inside the Irish president's residence, and turning to Higgins, he quoted his grandfather. "Your feet will bring you to where your heart is," said Mr. Biden, added that it was an "honor to return and to come home to the home of my ancestors." 

The Good Friday Agreement encouraged both sides in the conflict to lay down arms and set up a local government for Northern Ireland, sharing power between Republicans and unionists. But his visit comes as tensions are running high, with trade issues after Brexit creating political fissures that prompted British unionist politicians to withdraw from a power-sharing government last year. Despite the signing of a new trade deal between the U.K. and the EU last month, Northern Irish unionists are refusing to return to the government. 

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The president's trip to Ireland also comes amid international fallout over the apparent leak of classified Pentagon documents online. Federal law enforcement officials have identified the person suspected of leaking secret defense and intelligence documents that have circulated online for weeks, three U.S. officials tell CBS News. The officials confirmed the suspect is a man named Jack Teixeira. The New York Times, which first revealed his name Thursday, reported that he is a 21-year-old member of the 102nd Intelligence Wing of the Massachusetts Air National Guard.

The president took his first questions on the subject Thursday before news of the suspect's identity broke, saying he's "concerned that it happened." 

"I'm not concerned about the leak because — I'm concerned that it happened, but there's nothing contemporaneous that I'm aware of that is of great consequence," Mr. Biden said. 

The U.S. president has long touted his Irish heritage, and the White House has made a point of hosting elaborate celebrations on St. Patrick's Day. Mr. Biden hosted Irish Prime Minister Leo Eric Varadkar at the White House for St. Patrick's Day last month, complete with a performance by Niall Horan of One Direction.

Mr. Biden is the eighth sitting U.S. president to visit Ireland. John F. Kennedy, the first Irish-Catholic president, was the first sitting U.S. president to visit. Mr. Biden's sister, Valerie — his "best friend in the world," and his adult son, Hunter, are traveling with the president.

On Friday, the president is set to travel to County Mayo, where his great-great-great grandfather was born in the 1840s. He plans to visit a sanctuary and genealogical center before delivering remarks at a cathedral, according to the White House.

"Today, ladies and gentlemen, as we celebrate the enduring partnership between our nations, our shared past, our present, let's set our eyes squarely on the future," Mr. Biden said as he closed out his remarks to the parliament Thursday. "Let's harness what's best in us — our courage, our creativity, our loyalty, our tenacity, and our loyalty again. Let's once more, for our generation and the generation to come, strive to make hope and history rhyme. Because I've never been more optimistic about the future than I am today. And I'm at the end of my career, not the beginning."

Haley Ott contributed to this report.

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Kathryn Watson

Kathryn Watson is a politics reporter for CBS News Digital based in Washington, D.C.