Sept. 11: Trump, Biden Mark 19th Anniversary Of Attacks While President Trump spoke in Shanksville, Pa., Democratic presidential candidate Joe Biden bumped elbows with Vice President Pence in New York. Biden is traveling to Shanksville later in the day.

'America Will Always Rise Up': Trump, Biden Commemorate Sept. 11 Attacks

President Trump and first lady Melania Trump attend a ceremony commemorating the 19th anniversary of the Sept. attacks in Shanksville, Pa., on Friday. Brendan Smialowski/AFP via Getty Images hide caption

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Brendan Smialowski/AFP via Getty Images

Updated at 2:04 p.m. ET

Friday marks the 19th anniversary of the Sept. 11, 2001, attacks against the United States — the single deadliest instance of a terrorist attack in world history and among the most consequential global policy markers in modern times.

President Trump and first lady Melania Trump attended a morning observance in Shanksville, Pa., where United Flight 93, believed to be headed toward to Washington, D.C., crashed, killing all 40 passengers and crew on board. Former Vice President Joe Biden visited the site later Friday, laying a wreath at the memorial marking the victims' names.

At the earlier ceremony, Trump said, "The heroes of Flight 93 are an everlasting reminder that no matter the danger, no matter the threat, no matter the odds, America will always rise up, stand tall, and fight back."

A U.S. Park Ranger moves a memorial wreath prior to President Trump delivering remarks at the Flight 93 National Memorial on Friday. Jeff Swensen/Getty Images hide caption

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Jeff Swensen/Getty Images

Trump spoke of "our undying loyalty to the nearly 6 million young men and women who have enlisted in the United States Armed Forces since Sept. 11, 2001. More than 7,000 military heroes have laid down their lives since 9/11 to preserve our freedom. No words can express the summit of their glory or the infinite depth of our gratitude. But we will strive every single day to repay our immeasurable debt and prove worthy of their supreme sacrifice."

The somber remarks were notable in light of reports that Trump disparaged service members who were killed in World War 1 as "suckers" and losers," and also denigrated top military leaders.

Vice President Pence and Biden, the Democratic presidential nominee, both attended a memorial service Friday morning at the site of the World Trade Center, whose twin towers were destroyed in the attack. The two bumped elbows in greeting.

Pence read Psalm 23 from the Bible.

Earlier, Biden told reporters that he was "not going to talk about anything other than 9/11. We took all our advertising down. It's a solemn day. That's how we're going to keep it."

Democratic presidential candidate Joe Biden greets Vice President Pence at the 9/11 Memorial in New York to commemorate the 19th anniversary of the Sept. 11 attacks on Friday. Angela Weiss/AFP via Getty Images hide caption

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Angela Weiss/AFP via Getty Images

Democratic presidential candidate Joe Biden greets Vice President Pence at the 9/11 Memorial in New York to commemorate the 19th anniversary of the Sept. 11 attacks on Friday.

Angela Weiss/AFP via Getty Images

Asked by a reporter at ground zero what the day means to him, Biden said, "It means I remember all my friends that I lost. It takes a lot of courage for someone that lost someone to come back today," Biden continued. "I know from experience, losing my wife, my daughter, my son, you relive it, the moment as if it's happening. It's hard. It's a wonderful memorial, but it's hard. It just brings you back to the moment it happened, no matter how long, how much time passes. So I admire the families who come."

Democratic vice presidential nominee Kamala Harris took part in a ceremony in Fairfax, Va. She said she was at the gym on the morning of Sept. 11 when the attacks occurred. "Everyone got off their equipment and we all stood around in utter disbelief," she said.

"What our attackers failed to understand was that the darkness they hope would envelop us on 9/11 instead summoned our most radiant and defined human instincts — the instinct to care for one another, to transcend our divisions and see ourselves as fellow citizens," she said. "The instinct to unite."

Nearly 3,000 people were killed when adherents to the Islamic extremist group, al-Qaida, hijacked four commercial airliners and crashed them across the eastern part of the country.

The twin towers of the World Trade Center in New York City crumbled and the Pentagon in Virginia was seriously damaged, resulting in thousands of deaths and countless additional long-term health and financial hardships for victims and first responders.

Before the ceremony at ground zero, according to a pool report, Biden comforted an elderly woman using a wheelchair who was holding a picture of her son. She told Biden he had died in his early 40s. Biden took the image and looked it over, reflecting on losing his own son Beau. "It never goes away," Biden said. She repeated his words.

The woman, 90 and perhaps joking, told Biden she was entering her "last year," at which point her daughter suggested she knock it off. "You don't know that, Mom!" she said.

"You and I will be here next year," Biden assured the woman, then looked at her daughter.

Democratic presidential candidate Joe Biden greets Maria Fisher, 90, whose son Andrew Fisher was killed in the World Trade Center's north tower 19 years ago. Amr Alfiky/Pool/AFP via Getty Images hide caption

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Amr Alfiky/Pool/AFP via Getty Images

Pence stopped at a fire station and spoke with firefighters there, according to a pool report.

"It's an honor for us to be here today," Pence said, to "pay a debt of gratitude."

"I must tell you I was in Washington, D.C., on that day. I saw the sky filled there with smoke," he said.

"Like every other American, I watched. I watched as the towers burned. I watched as people rightly ran out and you ran in."

You "considered the lives" of people "in the towers more important than your own," he said.

A military honor guard stands on the South Lawn of the White House on Friday as staff members hold a moment of silence in honor of those killed in the Sept. 11 attacks. Drew Angerer/Getty Images hide caption

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Drew Angerer/Getty Images

The events of Sept. 11 shifted the course of U.S. foreign policy and launched the controversial U.S.-led war on terror — a years-long, financially costly and ethically contentious conflict that has seen the United States deploy thousands of military personnel and pour considerable resources into stemming the tide of extremism in the Middle East.

Recent presidential candidates have made minimizing the U.S. role in a perpetual war a major pitch to voters, who, in the case of younger ones, have lived most — if not all — of their lives with the nation involved in a global armed conflict.

The two most recent presidents, Barack Obama and Trump, have each lodged what they have considered significant wins in the fight against global terror: respectively, the 2011 killing of Osama bin Laden, who orchestrated the Sept. 11 attacks, and the 2019 special operations mission that killed Abu Bakr al-Baghdadi, leader of the Islamic State group.

While global terror has thus far played a more understated role in the 2020 White House campaigns, ongoing unrest in the Middle East and Americans' lingering memory of the unprecedented 2001 attacks continue to influence U.S. policy at home and abroad.