Victor Davis Hanson: ‘Donald Trump’s shocking Obama and Biden attack shows he won’t play by the rules’

"You could see the faces of our former presidents... they thought, 'oh my God, this man is a revolutionary," Hanson said.

Hanson described how Trump laid out his "plan of attack", including ending illegal immigration, addressing "anchor babies" through reinterpreting the 14th amendment, and stopping "catch and release" policies.

The historian said the former presidents are all fearful of their legacies being scuppered by Trump.

"Everybody thought he would hold back, but he doesn't play by the markers of the Queensbury rules," Hanson said of Trump's approach to addressing his predecessors.

Trump's inauguration speech included several dramatic policy announcements, including plans to rename the Gulf of Mexico to the "Gulf of America".

The former president also declared there would only be two recognised genders - male and female - and announced US withdrawal from both the Paris climate agreement and World Health Organisation.

He pledged to sign approximately 200 executive orders on his first day, including measures to tackle illegal immigration and declare cartels as foreign terrorist organisations.

Trump also vowed to pursue a new era of oil and gas exploration, declaring "drill, baby, drill".

During the ceremony, former presidents displayed visible reactions to Trump's declarations. Obama was caught asking Bush "How can we stop what's happening?", prompting chuckles from the 43rd president.

Hillary Clinton was seen laughing during Trump's announcement about renaming the Gulf of Mexico.

Later that evening, Trump revealed which former president he would seek advice from, praising Bill Clinton as having "a great political sense" while notably excluding Obama and Bush.

Hanson explained Trump's confrontational approach stemmed from his treatment by his predecessors and political opponents.

"They impeached me twice. They tried to get me off the ballot. They waged lawfare in five different jurisdictions against me," Hanson quoted Trump's perspective.

"His view of the world is these people are pretty nasty... they're not nice people and I'm not going to play by their rules, I'm going to call them out for what they are," the historian added.