NEW YORK • No one could mistake the voice of David McCullough, either in the books that have made him one of the most influential United States historians of his era or in the documentaries he has narrated for the American Experience television series.
He typically strikes a tone of determined neutrality. In public appearances, he said, he avoids commentary on contemporary politics.
"Very often, during question-and- answer sessions, people ask me some question about the president or other would-be candidates," he said recently. "I've always said, 'My speciality is dead politicians.' In that way, I could sidestep the question without getting myself involved.
"But this time around, I don't feel that way anymore."
Now McCullough and film-maker Ken Burns have assembled a group of distinguished US historians to speak about the candidacy of Mr Donald Trump, the presumptive Republican presidential nominee, in videos being posted to a Facebook page, Historians On Donald Trump.
It includes, among others, Ron Chernow, Professor David Levering Lewis, Dr William E. Leuchtenburg and Dr Vicki Lynn Ruiz and speaks with alarm about Mr Trump's candidacy and his place in the march of US history.
McCullough, raised in a Republican home and now aligned with no party, said the prospect of a Trump presidency so distressed him, he felt he could not remain publicly detached. "When you think of how far we have come, and at what cost and with what faith, to just turn it all over to this monstrous clown with a monstrous ego, with no experience, never served his country in any way - it's just crazy," he said. "We can't stand by and let it happen."
He said he contacted Burns after seeing him tell this year's graduating class at Stanford University that despite 40 years of avoiding advocacy in his work, he no longer had "the luxury of neutrality or 'balance' or even bemused disdain".
After a few conversations, McCullough said, they came up with a plan. "Why don't we see if we can round up some other people who care about the American story, and who have given so much of their life's work to it, see if they are willing to step out and make themselves heard."
The videos are mostly homemade, smartphone productions. None of the historians asked to weigh in has declined, Burns said.
Like many of the others, he added that he heard echoes of dangerous populist demagogues in Mr Trump's rhetoric. Among the issues that were cited were his calls to ban all Muslims, his characterisation of many Mexicans as criminals and his mockery of veterans and people with disabilities.
Mr Trump has said the country faces crises that require strong action to protect its borders and that his role as an outsider has cost him the approval of elites and entrenched interests.
In the 1920s, fear of immigrants fuelled the rise of the Ku Klux Klan and exclusionary laws aimed at European Catholics and Asians, said Dr Ruiz, a professor of history at the University of California, Irvine, and past president of the American Historical Association.
Also, about one-third of the Mexican population in this country was pushed out, more than half of them US citizens by birth, she said. "Playing with hate has had tragic consequences throughout our history."
Chernow, a Pulitzer Prize winner whose Alexander Hamilton was a principal source for the Broadway musical Hamilton, had been struck by Mr Trump's lack of reference to the founding documents of American history, or to presidents such as George Washington, Abraham Lincoln and Franklin D. Roosevelt.
"The only historical movement Trump alludes to is a shameful one - America First," Chernow said, recalling an isolationist political organisation at the time Nazi Germany was taking power across Europe.
Dr Leuchtenburg, a professor emeritus at the University of North Carolina at Chapel Hill and a leading scholar of the US presidency, said Mr Trump was essentially ahistorical. "He has no sense of the American past," he said. "He doesn't understand the achievements of this country."
NEW YORK TIMES