While being sworn in by Supreme Court Chief Justice John Roberts, Trump held one hand in the air and the other by his side.
His wife Melania was holding two Bibles for the president to take his oath with, but he did not touch them.
Whether this was a conscious decision or an oversight is unknown, but the oath appears to have been somewhat rushed.
Mrs Trump was not yet at her husband’s side when he was asked to raise his right hand.
And the president’s children were still moving into place as the oath was being recited.
After taking the oath, Trump shook hands with Roberts and former President Joe Biden, then greeted his children.
While presidents are not constitutionally required to put their hands on the Bible, it has been done by almost every president.
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Thomas Jefferson, Calvin Coolidge and Theodore Roosevelt did not put their hands on a Bible, and John Quincy Adams swore his oath on a book of law.
There was no Bible nearby when Lyndon Johnson was sworn in after the assassination of John F Kennedy. Instead he took the oath on a book of Catholic liturgy.
But unlike his predecessors, Trump was standing directly beside his wife holding two Bibles.
The first was Trump’s personal Bible, and the second was the Bible Abraham Lincoln used to be sworn in in 1861.
Vice President JD Vance took his oath on a family Bible held by his wife Usha.
When Trump took the oath of office the first time around in 2017, he did put his hand on the Bible.
Sons Donald Jr, Eric, and Barron, as well as daughters Tiffany and Ivanka were all the attendance at the inauguration.