WASHINGTON — In President Donald Trump’s latest exhortation to his faithful supporters, he told them: “Don’t believe the crap you see from these people, the fake news,” adding: “Just remember: What you’re seeing and what you’re reading is not what’s happening.”

He was referring to mainstream journalism outlets not on the right wing, notably cable television platforms such as CNN and MSNBC and newspapers such as The New York Times and The Washington Post, which are his most avid critics and fact checkers.

They and some other less liberal news organizations like The Wall Street Journal have demonstrably been truth police, holding Trump to a standard of verification to which he frequently and even regularly falls miles short.

With typical brashness, the president himself is a chief practitioner and purveyor of fake news, even to the point of peddling a transparently fictional “clarification” of his alarming statement at the recent Helsinki summit with Russian President Vladimir Putin.

Standing next to Putin in Helsinki, Trump said, “I don’t see any reason why it would be” Russia involved in the 2016 elections meddling. A day later in Washington Trump averred he meant say “wouldn’t be” — a claim as shocking as it was laughable.

Trump’s subsequent advice at a campaign-like rally of Trump worshippers to boycott or at least disbelieve what they see or hear on the mainstream news media very likely was a case of preaching to the choir. Many if not most of his true believers routinely depend, as he regularly does, on Trump-friendly Fox News, whose most prominent commentators, like his fawning pal Sean Hannity, are conspicuously in the president’s pocket.

Just the other day, major newspapers editorially critical of the president reported that on Air Force One, first lady Melania Trump was seen watching CNN on the plane’s television set, to her husband’s ire. If true, it was a sign of wifely independence and a breach of the commonplace staff loyalty to conservative news media in Trump World.

Political independence and absence of bias have long been conceits of the Fourth Estate, as the news business somewhat self-importantly refers to itself, as if to elevate itself to the realm of the three branches of American government. But many, particularly conservatives, contend otherwise.

For reporters, covering the political beat is generally regarded a prize assignment. Ideally, they are expected to leave their personal political views at the door, except for opinion writers and commentators, who inevitably are known as much for their leanings as for their smoothness of delivery, or lack thereof.

But a press card is more than something their movie impersonators stick in their fedoras. It a constitutional protection under the First Amendment and usually one stoutly defended by members of all political parties.

Donald Trump is hardly the first major American political figure to declare war on mainstream journalism. In our time, the likes of Huey Long, Joe McCarthy, George Wallace, Richard Nixon and Spiro Agnew all were known and even gained wide public support for their tussles with the press.

Agnew and one of his favorite speechwriters, William Safire — later a columnist for the New York Times — warmed conservatives’ hearts and earned some disdain in the press by labeling reporters “nattering nabobs of negativism.”

But seldom, until Trump, has a major American politician been successful in generating wide public contempt and disfavor for what one of them used to call “squalid little men with dirty fingernails scribbling in their notebooks.”

In the era of Trump, men and women herded into press sections by campaign operatives are frequently subjected to ugly and profane verbal abuse as “enemies of the people.” All they are guilty of is conveying to the public at large, contrary to Trump’s allegations, “what they’re seeing and what’s happening.”

But most of today’s reporters have developed thick skin, and in the service of the public’s right to know they will continue to report on the president’s contemptuous serial lying.

Editor’s note: Jules Witcover’s latest book is “The American Vice Presidency: From Irrelevance to Power,” published by Smithsonian Books. You can respond to this column at juleswitcover@comcast.net.