On a visit to Europe to mark the 100th anniversary of the end of the first world war, Donald Trump insisted to his then chief of staff, John Kelly: “Well, Hitler did a lot of good things.”

The remark from the former US president on the 2018 trip, which reportedly “stunned” Kelly, a retired US Marine Corps general, is reported in a new book by Michael Bender of the Wall Street Journal.

Frankly, We Did Win This Election has been widely trailed ahead of publication next week. The Guardian obtained a copy.

Bender reports that Trump made the remark during an impromptu history lesson in which Kelly “reminded the president which countries were on which side during the conflict” and “connected the dots from the first world war to the second world war and all of Hitler’s atrocities”.

Bender is one of a number of authors to have interviewed Trump since he was ejected from power.

He reports that Trump denied making the remark about Hitler.

But Bender says unnamed sources reported that Kelly “told the president that he was wrong, but Trump was undeterred”, emphasizing German economic recovery under Hitler during the 1930s.

“Kelly pushed back again,” Bender writes, “and argued that the German people would have been better off poor than subjected to the Nazi genocide.”

Bender adds that Kelly told Trump that even if his claim about the German economy under the Nazis after 1933 were true, “you cannot ever say anything supportive of Adolf Hitler. You just can’t.”

Trump ran into considerable trouble on the centennial trip to Europe, even beyond his usual conflicts with other world leaders.

A decision to cancel a visit to an American cemetery proved controversial. Trump was later reported to have called American soldiers who died in the war “losers” and “suckers”.

Kelly, whose son was killed in Afghanistan in 2010, left the White House in early 2019. He has spoken critically of Trump since, reportedly telling friends the president he served was “the most flawed person I have ever met in my life”.

Bender writes that Kelly did his best to overcome Trump’s “stunning disregard for history”.

“Senior officials described his understanding of slavery, Jim Crow, or the Black experience in general post-civil war as vague to nonexistent,” he writes. “But Trump’s indifference to Black history was similar to his disregard for the history of any race, religion or creed.”

Concern over the rise of the far right in the US grew during Trump’s time in power and continues, as he maintains a grip on a Republican party determined to obstruct investigations of the deadly 6 January assault on the US Capitol by supporters seeking to overturn his election defeat.

Trump has made positive remarks about far-right and white supremacist groups.

During a presidential debate in 2020, Trump was asked if he would denounce white supremacists and militia groups. He struggled with the answer and eventually told the far-right Proud Boys group to “stand back and stand by”.

In 2017, in the aftermath of a neo-Nazi march in Virginia which earned supportive remarks from Trump, the German magazine Stern used on its cover an illustration of Trump giving a Nazi salute while wrapped in the US flag. Its headline: “Sein kampf” – his struggle.