Before he ran president, Joe Biden bitterly criticized President Donald Trump, expressing his frustration with his leadership according to a new book.

When Biden spoke to his team about running for president in 2020, he cited Trump’s presidency as his biggest reason.

“This guy just isn’t really an American president,” Biden said.

US President Donald Trump speaks to the troops during a surprise Thanksgiving day visit at Bagram Air Field in Afghanistan. (OLIVIER DOULIERY/AFP via Getty Images).

The comment was recalled by Biden’s political adviser Ron Klain who was present for the meeting in the book, Peril by Bob Woodward and Robert Costa.

Biden was deeply unsettled by Trump’s presidency, especially after his comments about the riots in Charlottesville.

“I just feel like I have to do this,” Biden said. “Trump represents something fundamentally different and wrong about politics.”

The book also recounts other incidents of Biden’s views on Trump behind the scenes.

After Biden was inaugurated as president, he walked into one of the rooms in the White House where Trump had set up a large video screen to practice golf.

US President Joe Biden checks his watch as they attend the dignified transfer of the remains of one of the 13 fallen servicemembers who died in a terrorist attack in Kabul during the botched evacuation. (SAUL LOEB/AFP via Getty Images).

“What a fucking asshole,” Biden commented.

The Biden team also hated using Trump’s name, the book reports, warning each other to avoid the “T word” in their daily routines.

Even eight months later, Trump continues to weigh heavily on Biden’s mind.

In September, Biden appeared aware that Trump had spoken about entering the boxing ring with the president as part of a promotional interview for a fight.

“I mean — you know. I should be so lucky,” Biden told reporters. “You know what I mean?”