NEW YORK (AP) — With presidential candidates looking on, some 9/11 victims' relatives appealed to them Wednesday for accountability as the U.S. marked an anniversary laced with election-season politics.

In a remarkable tableau, President Joe Biden, former President Donald Trump and Vice President Kamala Harris stood together at ground zero just hours after Trump and Harris faced off in their first-ever debate. Trump and Biden — the successor whose inauguration Trump skipped — shook hands, and former New York Mayor Michael Bloomberg appeared to facilitate a handshake between Harris and Trump.

Then the presidential rivals stood only a few feet apart, Biden and Bloomberg between them, as the observance began with the tolling of a bell and a moment of silence. At Trump's side was his running mate, Sen. JD Vance.

The image was one of putting politics aside at another solemn commemoration of the hijacked-plane attacks that killed nearly 3,000 people on Sept. 11, 2001. For years, politicians have been only observers at ground zero commemorations, the microphones going instead to relatives who read victims' names aloud.

Some of those readers took the occasion Wednesday to deliver political messages of their own.

"We are pleading for your help, but you ignore us," Allison Walsh-DiMarzio said, directly challenging Trump and Harris to press Saudi Arabia about any Saudi official involvement in the attacks. Most of the 19 hijackers were Saudi, but the kingdom denies involvement by senior Saudi officials.

"Which one of you will have the courage to be our hero? We deserve better," Walsh-DiMarzio said. She's a daughter of 9/11 victim Barbara P. Walsh, an administrative assistant.

Joanne Barbara was one of multiple readers who spoke out against a now-revoked plea deal that military prosecutors struck with alleged 9/11 mastermind Khalid Sheikh Mohammed and two fellow defendants.

"It has been 23 years, and the families deserve justice and accountability," said the widow of Assistant Fire Chief Gerard Barbara.

Biden, on the last Sept. 11 of his term and likely his half-century political career, was headed with Harris later to ceremonies in Pennsylvania and at the Pentagon, the other two sites where commercial jets crashed after al-Qaida operatives seized them.

Trump and Vance moved on from World Trade Center ceremony to visit a New York City firehouse. Trump also was due later Wednesday at the Flight 93 National Memorial near rural Shanksville, Pennsylvania, where one of the planes crashed after crew members and passengers tried to wrest control from the hijackers. The names of those killed there were read aloud there Wednesday morning, and victims' relations spoke briefly.

The attacks killed 2,977 people and left thousands of bereaved relatives and scarred survivors. The planes took down the World Trade Center's twin towers and carved a gash in the Pentagon, the U.S. military headquarters, where an American flag was unfurled at dawn Wednesday in tribute.

While it may seem that many Americans don't observe 9/11 anniversaries anymore, "the men and women of the Department of Defense remember," Defense Secretary Lloyd Austin said.

The attacks altered U.S. foreign policy, domestic security practices and the mindset of many Americans who had not previously felt vulnerable to attacks by foreign extremists.

Effects rippled around the world and through generations as the U.S. responded by leading a " Global War on Terrorism," which included invasions of Afghanistan and Iraq. Those operations killed hundreds of thousands of Afghans and Iraqis and thousands of American troops.

Communities around the country hold their own 9/11 remembrances. Volunteer projects also mark the anniversary, which Congress has titled both Patriot Day and a National Day of Service and Remembrance.

During early anniversaries at ground zero, presidents and other officeholders read poems, parts of the Declaration of Independence and other texts.

But the National Sept. 11 Memorial and Museum decided in 2012 to limit the ceremony to relatives reading victims' names.

If politicians "care about what's actually going on, great. Be here," Korryn Bishop said as she arrived to watch Wednesday's ceremony.

"If they're just here for political clout, that upsets me," added Bishop. She lost her cousin John F. McDowell Jr., who worked in finance..

Brandon Jones was glad politicians weren't on the podium.

"This should be a site for coming together to find feasible solutions and peace. This should not be a place to score political points to get brownie points to round up your base," said Jones. He's a cousin of victim Jon Richard Grabowski, an insurance firm technology executive.

In 2008, then-senators and presidential campaign rivals John McCain and Barack Obama paid their respects at ground zero, which was still an open pit.

The anniversary became a fraught part of the 2016 presidential campaign. The Democratic nominee, former Secretary of State Hillary Clinton, abruptly left the trade center ceremony, stumbled while awaiting her motorcade and later disclosed that she had been diagnosed with pneumonia. The episode stirred fresh attention to her health, which her Republican opponent — Trump, who was also at the observance — had been questioning for months.

Over the years, some of the relatives who read victims' names have used the forum to bemoan Americans' divisions, exhort leaders to prioritize national security, acknowledge the casualties of the war on terror, complain that officials are politicizing 9/11 and even criticize individual officeholders. Others appeal for peace.

"It's my prayer that this wicked act called terrorism will never occur again," Jacob Afuakwah said Wednesday. He lost his brother, Emmanuel Akwasi Afuakwah, a restaurant worker.

But most stick to tributes and personal reflections. Increasingly they come from children and young adults who were born after the attacks killed one of their relatives.

Thirteen-year-old twins Brady and Emily Henry never got to meet their uncle, firefighter Joseph Patrick Henry.

"We promise to continue telling your stories," Emily said, "and we'll never let anyone forget all those lost on Sept. 11."

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Contributing were Associated Press journalists Julie Walker, Adriana Gomez Licon in New York and Tara Copp in Washington, and Bruce Shipkowski in Toms River, New Jersey.