The 2016 Republican presidential primary season seems like a long, frightening dream. Except the source of terror is real. It comes in the form of Donald John Trump Sr. — the white man’s Marion Barry — who stands a good chance of becoming the Republican nominee for president of the United States. A nightmare awaits.

How could it be otherwise? If ever bestowed presidential powers, Trump would be in a position to inflict great harm on the nation and world.

To think: Trump is closer to reaching the White House than any other Republican beneath our spacious skies or above our fruited plain.

And to think: Ruling-class politicians and pundits muffled their guffaws when he announced his presidential run in June. Here Trump stands, vilified but triumphant, basking in the support of hordes of Republicans, holding the upper hand over a vanquished Republican establishment.

The poor souls were clueless.

Had the GOP intelligentsia paid attention to our nation’s capital during Barry’s reign as mayor and council member, they might have seen Trump coming. Could it be that Trump is Barry in disguise?

Trump, as Barry demonstrated during his years of melodrama, operates as though he is free to do as he wants to a fare-thee-well. He is a Drama King who falls, gets up and gallops off into another battle — often conflicts of his own making, all under the glare of a media that can’t get enough.

Trump, as did Barry, has amassed devoted followers who swear by and believe in him, no matter what. Trump, like Barry, enjoys a faith and trust to make his competition drool.

Both men responded to a call, heard by them alone, to seek political power. And they received adulation from people who believed the man knew them, respected and spoke for them, in a language that the powerbrokers would not otherwise have heard.

Unlike the rest of the field, Trump, as with Barry, has no hesitancy about displaying his longings, ambitions, appetites and passions. Both, too, made line-crossing a staple of their careers.

Before Trump got started in on immigrants, Barry took off against them: He famously complained about “immigrants . . . particularly from the Philippines.”

“Intolerant and narrow-minded,” said Jose L. Cuisia Jr., the Philippines’ ambassador. Barry, as Trump would do years later, shrugged it off.

Barry had a method to his madness. So does Trump. He understands the people he speaks for. He is the hero who fights battles that they, the powerless, cannot fight themselves.

Barry taunted the white enemy. Trump taunts the brown and the brokers.

Both offered the gratifying joy of vicarious revenge without the attendant penalties of a real encounter — behavior captured by the late African American psychologist Kenneth Clark in his dissection of black Harlem’s old-style politician Adam Clayton Powell.

Hear Clark’s description of Powell, and think Barry and Trump:

“The . . . masses do not see Powell as amoral but as defiantly honest.” What some “regard as Powell’s violation of elemental ethics, Negroes view as effective and amusing defiance.”

And this: “He seems a simple hedonist above all else. He appears free of any sense of guilt. Guilt is the consequence of a sense that one has violated what one believes in, a consequence of behavior in conflict with one’s conscience. To be rid of such conflict is to be free of much anguish.” Think Trump and Barry, both worry-free and unencumbered by principle.

Barry, like Trump today, was frequently criticized in newspaper editorials. Those editorials only strengthened Barry’s appeal among some D.C. residents. So it is with Trump, because condemnation by respectable newspapers is taken as evidence of Trump’s effectiveness. Clearly editorial writers would not be concerned with an impotent politician.

That’s what Barry understood and used to gain power. That’s what Trump uses.

The person standing in Trump’s way to the GOP throne is Ted Cruz, who seems not to be running for the Republican nomination but for Commandant of the Police State.

Cruz stops short of Trump’s call for a total shutdown of Muslims entering the United States or the mass deportation of 11 million undocumented immigrants or violation of the Geneva Conventions (said Trump on terrorists: “take out their families”).

But anti-Muslim Cruz wants law enforcement to “patrol and secure Muslim neighborhoods before they become radicalized.” Why spend all that money and personnel on special patrols of Muslim neighborhoods — if, in fact, would-be terrorists can be identified? What’s the next step? Roundups and relocation to internment camps?

This lover of religious liberty who smears a religion and demonizes its followers is also a major contender for president of the United States. That the Republican elite, in their mortal fear of Trump, are in the process of sucking up to Cruz is sickening.