President Joe Biden is making an appeal for the nation to reclaim the spirit of cooperation that sprung up in the days following the 9/11 terror attacks as he commemorates those who died 20 years ago.

Biden was a senator when hijackers commandeered four planes and exacted the nation’s worst terror attack in 2001. Now he marks the 9/11 anniversary for the first time as commander in chief.

The president planned to pay his respects at the trio of sites where the planes crashed, but he was leaving the speech-making to others.

Instead, the White House released a taped address late Friday in which Biden spoke of the “true sense of national unity” that emerged after the attacks, seen in “heroism everywhere — in places expected and unexpected.”

“To me, that’s the central lesson of September 11,” he said. “Unity is our greatest strength.”

Biden arrived in New York on Friday night as the skyline was illuminated by the “Tribute in Light,” hauntingly marking where the towers once stood. His first stop on Saturday was to be the National September 11 Memorial, where the twin towers of the World Trade Center were toppled as a horrified world watched on television.

From there he was to visit the field near Shanksville, Pennsylvania, where a plane fell from the sky after heroic passengers fought terrorists to prevent it from reaching its Washington destination. And finally, he was headed to the Pentagon, where the world’s mightiest military suffered an unthinkable blow to its very home.

Biden’s task, like his predecessors before him, was to mark the moment with a mix of grief and resolve. A man who has suffered an immense personal tragedy, Biden speaks of loss with power.

He gave voice to the pain that comes with memories of 9/11 in his video message, saying, “No matter how much time has passed, these commemorations bring everything painfully back as if you just got the news a few seconds ago.”

Robert Gibbs, who served as President Barack Obama’s press secretary, said that for Biden, “It’s a moment for people to see him not as Democratic president, but as president of the United States of America,.”

“The American people are somewhat conflicted about what they have seen out of Afghanistan the last couple of weeks,” Gibbs said. “For Biden, it’s a moment to try to reset some of that. Remind people of what it is to be commander in chief and what it means to be the leader of the country at a moment of such significance.”

On the 20th anniversary of the attacks, Biden now shoulders the responsibility borne by his predecessors to prevent future tragedy and must do so against fresh fears of a rise in terror after the United States’ hasty exit last from the country from which the Sept. 11 attacks were launched.

Biden will be the fourth president to console the nation on the anniversary of that dark day, one that has shaped many of the most consequential domestic and foreign policy decisions made by the chief executives over the past two decades.