Republican presidential candidate Donald Trump speaks during an interview with the Associated Press in his office at Trump Tower in New York on May 10. (Mary Altaffer/Associated Press)

THE PAST weekend brought yet more evidence of Donald Trump’s contempt for truth and essential political standards. Yet the reality-television star continued to consolidate GOP support, a fact punctuated by Republican National Committee Chairman Reince Priebus’s tour on Sunday morning television, in which he argued that the “sort of traditional review and analysis of individual candidates has not applied to Donald Trump,” because Mr. Trump is a different kind of candidate — “a total outsider that’s going to cause an earthquake in Washington.”

In fact, it is all the more important that voters see Mr. Trump’s full business and financial record precisely because he lacks a history of public service on which to judge his suitability. How, then, can Mr. Priebus argue that basic standards, such as honesty and transparency, do not apply? Because, he explained, voters do not seem to care about them — at least not so far. And if voters don’t care, Mr. Priebus doesn’t care: “We want to win in November, and Donald Trump is someone who has been winning.”

This is not the first time that the chairman has exposed the rank nihilism that is driving Republican leaders’ acceptance of Mr. Trump, and Mr. Priebus is far from alone. Even Sen. John McCain (Ariz.) — a war hero whose service Mr. Trump ridiculed, a man who disagrees with Mr. Trump on issue after issue, not to mention on how the nation’s politics should be conducted — has somehow found his way to backing the billionaire. But winning cannot excuse lying, debasing the country’s politics and driving wedges among its people.

Last Friday, Mr. Trump denied that he had pretended to be his own spokesman, though in 1990 court testimony he admitted to using an alias “on occasion” — and though there is a convincing audiotape of Mr. Trump apparently posing as “John Miller” and detailing Mr. Trump’s supposedly crowded love life to a reporter. Taking on false identities may be merely weird; flat-out lies are more disturbing. As is so often the case, Mr. Trump asks voters to ignore evidence and reason based on nothing more than his say-so.

Similarly, Mr. Trump has said that he would release his tax returns, but he routinely evades questions about when that will happen. He told the Associated Press last week that he feels no obligation to release them before the election, and when asked what tax rate he paid, he told ABC News last Friday that it is “none of your business.” Presidential candidates’ tax information has been the public’s business for decades.

Rudimentary adherence to the truth and respect for openness matter. Mr. Priebus and his confederates in amorality dismiss or excuse Mr. Trump’s mockery of these precious political values because they believe politics matters more than principle. Mr. Trump’s campaign will end, one way or another, in November. The disgrace of the Republicans who have supported him will not.