Rivals for the White House displayed a moment of unity as the US marks the 19th anniversary of the 11 September 2001 terrorist attacks on Friday.
Democratic presidential nominee Joe Biden greeted Vice-President Mike Pence at the Ground Zero memorial in New York, where each attended ceremonies.
Mr Biden will travel to Shanksville, Pennsylvania – the site of the Flight 93 memorial – later to deliver remarks.
President Donald Trump spoke there earlier.
Though both 2020 candidates will speak in the same place, their schedules will not overlap, ensuring that Mr Biden and Mr Trump will not cross paths.
How is President Trump marking the anniversary?
Joined by First Lady Melania Trump, Mr Trump attended a morning service at the Shanksville memorial, where Flight 93 crashed after its 40 passengers and crew prevented hijackers from reaching the US Capitol building.
“To the family members of Flight 93: today every heartbeat in America is wedded to yours,” Mr Trump said. “Your pain and anguish is the shared grief of our whole nation.”
“The memory of your treasured loved ones will inspire America for all time to come. 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.”
Although both Mr Trump and Mr Biden will refrain from overt campaigning, their separate visits to Pennsylvania are being watched with close political scrutiny, as the state is seen as a key battleground to win in the November election.
Before his Shanksville visit, Mr Trump made a brief stop in Johnstown, Pennsylvania, to greet members of the state Army National Guard. The iron-and-steel town is in Cambria County – the heart of what has been known as ‘Trump country’ – in the southwest of the state.
Mr Trump spoke with three officers about local military and thanked them for their service, local media reported.
He narrowly beat Hillary Clinton in the state in 2016. “With the election less than eight weeks away, the president is fighting hard to keep the town on his side, and his visit underscores his effort,” says BBC’s Tara McKelvey.
Where is Biden?
Mr Biden and his wife, Jill, attended a memorial service and commemoration ceremony at the 9/11 museum in New York City, where, in 2001, attackers flew hijacked planes into the World Trade Center.
They will travel to Shanksville later in the afternoon to visit the same memorial as Mr Trump.
Mr Biden told reporters on Friday he would not talk about anything other than 9/11 and that his campaign had withdrawn political adverts from airing on television.
“We took all our advertising down, it’s a solemn day, and that’s how we’re going to keep it,” he said.
Mr Biden greeted Mr Pence at the World Trade Center site in New York earlier in the day, and the pair touched elbows in lieu of a handshake to observe protocols aimed at preventing the spread of coronavirus.
What’s the reaction?
Mr Pence delivered short remarks in New York City and read passages from the Bible, saying: “I pray these ancient words will comfort your hearts and ours.”
New York Governor Andrew Cuomo, a Democrat, also joined Mr Pence and Mr Biden at the memorial service.
On US Twitter, hashtags relating to 9/11 are trending, with people remembering the day and sharing stories of loved ones lost in the attacks.
Some on social media have also drawn attention to the anti-Muslim sentiment that spread across the country in the wake of 9/11, noting how they were bullied, stereotyped, or policed.
Hate crimes rose against Muslims after the 2001 attacks, FBI data found.
What happened on 9/11?
Nearly 3,000 people died when four hijacked airliners were crashed into the World Trade Center in New York, the Pentagon and the field in Shanksville, Pennsylvania on 11 September 2001.
Some 400,000 people were injured or exposed to other contaminants in the aftermath of the attacks, according to the US Centers for Disease Control.
Hundreds of first responders and survivors have died in the years since due to related illnesses, like cancer.
Weeks after the attack, the US sent troops to Afghanistan to combat the al-Qaeda terror group, which claimed responsibility for the attacks. The so-called ‘War on Terror’ has stretched decades and American intervention in the Middle East continues to be a quagmire of US foreign policy.