Washington • Forget it, America. It’s Chinatown.

Washington, once the guarantor of American values, is a crime scene. This capital of white marble is now encircled by yellow tape, rife with mendacity, cowardice and corruption. It’s Chinatown on the Potomac.

Robert Towne, screenwriter of the 1974 classic “Chinatown,” wrote the movie as a eulogy to great things that were lost. He said that he was not conjuring a place on a map but a state of mind: the futility of good intentions.

Or, as Raymond Chandler, the premier chronicler of Los Angeles noir, once wrote: “We still have dreams, but we know now that most of them will come to nothing. And we also most fortunately know that it really doesn’t matter.”

“Chinatown” was set in 1937, right before the war. Like Jack Nicholson’s Jake Gittes, America was naive about the forces of real corruption, real evil.

Towne wrote the movie in the early ’70s, in the dark years of Vietnam, Watergate and Richard Nixon’s doomed second term. Roman Polanski directed it a few years after his pregnant wife, Sharon Tate, was butchered by the Manson family.

In his latest fascinating dive into Hollywood, “The Big Goodbye,” Sam Wasson dissects “Chinatown.” “What makes Chinatown so uniquely disturbing as an American metaphor is that it is so unlike the whiteness of Ahab’s whale or the greenness of Gatsby’s light,” he writes in the forthcoming book. “However illusory, these are totems of aspiration, of possibility.”

He says that “Chinatown,” by contrast, is black: It’s about terrible truths you can’t undo, about a cynical world where you can’t beat the house and money wins, where you think you’ve got it figured out and then you realize you’re dead.

Sound familiar?

The movie is a good metaphor for the Trump era, when you hope that this grotesquerie is an aberration but you worry that the bad guys have already won.

Even if Donald Trump is impeached, we know now that the Russians have figured out how to rig our elections — and our dictator-loving president doesn’t seem too disturbed about that.

What makes the metaphor so powerful is its unAmericanness. In democracy, we supposedly have the power. But in Chinatown, there’s nothing you can do. Forget it, Jake. It’s an oligarchy.

Is the impeachment inquiry the false hope, the cocky detective?

This was the week that made it glaringly clear that the president put his fragile ego, idiotic conspiracy theories and political prospects ahead of U.S. national security interests. But watching Mike Pence and Marco Rubio and the red firewall of Republican lawmakers pervert principles to protect Donald Trump elicits dread that there will be more lawlessness.

As John Huston’s Noah Cross says when Jake confronts him over his turpitude: “Most people never have to face the fact that at the right time and the right place they are capable of … anything.”

In this desolate scenario, is Nancy Pelosi Jake?

Not really. The speaker is anything but naive. She is well aware that Mitch McConnell — an icy film noir villain if there ever was one — will snuff out any threat that Trump will be ousted. (And don’t forget, as the House demands documents from the vice president in the impeachment inquiry, if Trump and Pence have to go, we’ll have our first Madam President.)

Trump biographer Michael D’Antonio predicted that being in the White House would distill Trump to his essence. And his essence, D’Antonio says, is a dark swirl of cruelty, violence and fear. That is on disturbing display in “Border Wars: Inside Trump’s Assault on Immigration,” the new book by New York Times reporters Michael D. Shear and Julie Hirschfeld Davis.

“Privately,” they wrote in an adaptation of the book in The Times, “the president had often talked about fortifying a border wall with a water-filled trench, stocked with snakes or alligators, prompting aides to seek a cost estimate. He wanted the wall electrified, with spikes on top that could pierce human flesh. After publicly suggesting that soldiers shoot migrants if they threw rocks, the president backed off when his staff told him that was illegal. But later in a meeting, aides recalled, he suggested that they shoot migrants in the legs to slow them down. That’s not allowed either, they told him.”

The sordid moment where we find ourselves is at once stunning and ineluctable: the House move to impeachment, Trump’s lunatic denials about his blatant transgressions and his even more lunatic bouts of self-incrimination.

Nothing good was going to happen when the spoiled attention addict was put in a position to demand the attention — and favors — of the whole world, or else.

As The Times’ Maggie Haberman pointed out: “He has led a consequence-free life despite enormously self-destructive behaviors over time. The divorces were marriages he wanted out of. The bankruptcies impacted his lenders most, not him. All of his behavior in 2016 ended with him winning the presidency. And the Mueller obstruction inquiry ended with no definitive answer.”

D’Antonio says Trump is “a man making his own nightmare come to pass. His performance with the Finnish president was a florid demonstration of his inner self. Enraged and irrational, he was incapable of hiding his contempt, which is ever-present, and heedless of his effect on others.

“Trump doesn’t know that people who don’t confront their demons are destined to be confronted by them.”

And what is a better description of a film noir spiral than that?

Maureen Dowd (CREDIT: The New York Times)

Maureen Dowd is a Pulitzer Prize-winning Op-Ed columnist for The New York Times.