Historians speak out on Trump.

[David] McCullough and Ken Burns, the filmmaker and author, have assembled a group of distinguished American historians to speak about the candidacy of Donald J. Trump, the presumptive Republican presidential nominee, in videos being posted to a Facebook page, Historians on Donald Trump.

It is a diverse, honored group — including, among others, Robert A. Caro, Ron Chernow, David Levering Lewis, William E. Leuchtenburg, Vicki Lynn Ruiz — that speaks with alarm about Mr. Trump’s candidacy and his place in the march of American history.

I plan to work my way through that whole page.

Mr. McCullough, raised in a Republican home and now aligned with no party, said the prospect of a Trump presidency so distressed him that 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. The Republican Party shouldn’t stand by and let it happen.”

He goes on to say that he’s an independent and has admired plenty of Republicans and this isn’t a party thing. I second that. If Trump were a Democrat I would loathe him just as much and even more (on account of how I want Dems to be better than that).

In the 1920s, fear of immigrants fueled the rise of the Ku Klux Klan and exclusionary laws aimed at European Catholics and Asians, said Ms. 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 United States citizens by birth, she said.

“Playing with hate has had tragic consequences throughout our history,” she said.

And other histories too. It’s never benign. Let’s not do it.