Seventeen years after the devastating 9/11 attacks, President Donald Trump heads to Pennsylvania on Tuesday to pay tribute, as his predecessors have done, to the men and women who died aboard hijacked Flight 93. Those aboard United Flight 93, told over the phone by their loved ones that two other passengers jets had smashed into New York's World Trade Center, tried to regain control of their aircraft.

The crash site was far short of the attackers' goal: the US capital. The passengers who died in Shanksville have been hailed as heroes ever since.

White House spokeswoman Sarah Sanders said Trump would put the emphasis on "remembering that horrific day... and certainly honoring the individuals who were not only lost that day, but also put their lives on the line to help in that process."

It is believed that the hijackers were hoping to use the plane to attack the Capitol, home to the US House of Representatives and the Senate. On that day in 2001, Congress was in full session.

Trump will be accompanied by his wife Melania on a day that has come to symbolize national unity -- and which should offer him a welcome respite from the political mayhem swirling around him in Washington.

Tuesday's trip comes on the day that investigative reporter Bob Woodward's scathing White House tell-all book "Fear" -- which paints a portrait of a man unable to handle the presidency -- hits stores.