Speaking at the Republican Jewish Coalition candidate forum on Dec. 3, Donald Trump drew the ire of a few audience members when he wouldn't clarify whether he recognized Jerusalem as the undivided capital of Israel. (Reuters)

“I’M A negotiator like you folks; we’re negotiators,” Donald Trump said to the Republican Jewish Coalition on Thursday. “Is there anybody that doesn’t renegotiate deals in this room? Perhaps more than any room I’ve ever spoken to.” At another point, he remarked, “I know why you’re not going to support me — because I don’t want your money.”

These comments aren’t as objectionable as Mr. Trump’s talk of registering Muslim Americans, a proposal he has toyed with in the weeks since the Paris terrorist attacks, or when he mocked the physical disability of a New York Times reporter who dared challenge him. But they are of a piece with Mr. Trump’s near-constant use of cheap stereotypes and insults.

Mr. Trump is corrosive to the U.S. political debate in at least two ways. One is his basic contempt for facts. Mr. Trump simply made up his recent claim that he watched “thousands and thousands” of Muslims celebrating in New Jersey on 9/11, later justifying it by claiming some of his supporters remember similar events. Mr. Trump’s approach to truth — it is whatever I want it to be — uniquely threatens the notion that people of different identities and experiences can nevertheless conduct a civil dialogue based on the universal language of observable fact. Without this rudimentary principle, the American experiment in multi-ethnic, religiously diverse democracy is doomed.

Second, if it weren’t already clear, his comments this week underscore that Mr. Trump sees people as caricatures and stereotypes to be poked at and exploited rather than as individuals with dignity. This not only insults people, reducing them to simple manifestations of gender, creed or ethnicity. It also undermines the very premise of American freedom: that individuals’ inherent worth entitles them to unalienable rights that no president can or should abridge — especially “leaders” who, like Mr. Trump, inflame some Americans’ suspicions and prejudices against minority groups for political gain.

These are among the reasons that no mainstream party should associate with Mr. Trump, let alone support him should he somehow claim the GOP nomination. Republican leaders such as House Speaker Paul D. Ryan (Wis.), Senate Majority Leader Mitch McConnell (Ky.) and the various GOP presidential candidates should say, now, that they would never endorse or vote for him.

Instead, despite some scattered criticism, prominent Republicans sit on the sidelines waiting for Mr. Trump to flame out. A common line is the one Mr. Ryan used last month — that “every one” of those running for the GOP nomination “would be a far better president than Hillary Clinton.” This is obviously wrong: Mr. Trump represents a fundamental threat to the country’s political fabric.

According to a National Republican Senatorial Committee memo The Post obtained and printed this week, the official GOP strategy should Mr. Trump win the nomination is to occasionally admit that he says indefensible things — candidates are told to say that their wives or daughters are offended by “wacky things” Mr. Trump says about women — but to avoid “piling on.” They should, moreover, “grab onto the best elements of [his] anti-Washington populist agenda,” such as his tirades against globalization. Republicans should seek to be “authentic, independent, direct, firm,” like Mr. Trump, the memo states. Sounding anything like Mr. Trump is a winning formula for ethical bankruptcy.