Donald Trump, you may have noticed, has proved to be an, uh, unorthodox presidential candidate.

That served the celebrity well in real estate, on TV and in a record primary field of 17 Republican candidates. He’s now on the precipice of becoming the nominee for the party of Lincoln’s 41st attempt to occupy the White House.

All indications now are that the billionaire businessman will not become the 24th GOP president, despite his fans’ fervor and a record number of primary votes. The indications include a wide range of consistent national and state polls showing him almost universally behind the Democrat.

Such surveys, of course, can change along with voters’ opinions as the campaign and upcoming convention/reality show reaffirm or reshape existing evaluations.

What seems unlikely to change, however, is Trump’s unpredictable, usually counterproductive behavior. So the growing question is: What if Trump’s idea of winning is electing Hillary Clinton? And devastating the GOP in the process?

We suggested 13 months ago that Trump was a Clinton stalking horse: Whether intentional or not, Trump’s candidacy will focus attention on him and elect the Democrat whom he’s long supported. Nothing has happened since to change our mind, save that another Clinton White House could be an unintended consequence of an enormous Trump ego that expands faster than the universe.

Trump and Hillary Clinton are longtime friends and supporters of liberal causes. He’s contributed generously to her campaigns and family foundation. Trump conferred with her husband just before announcing his candidacy.

More significant, though, is Trump’s behavior. Yes, it seems unpredictable. And that’s compelling as Sunday night entertainment. He has mocked the handicapped, POWs and a female anchor’s menstrual cycle, among other crude displays, with no apparent damage.

But Americans aren’t clicking a remote control for a TV pitchman. They mark a secret ballot for the world’s most powerful person. Showmanship and stage presence help, as Ronald Reagan proved. But will they choose as controller of the nation’s nuclear launch codes someone whose trademark phrase is “You’re fired!”?

Since locking up the requisite delegates to hijack the GOP, Trump has done everything possible to torpedo his campaign as a serious candidate — and help Clinton’s stumbling candidacy.

His fundraising is tardy and halfhearted. He’s being battered by millions of dollars’ worth of unanswered negative ads like the ones that bloodied Mitt Romney beyond repair in 2012. His campaign staff turmoil dominated June news.

Trump’s done little to unify a fractured GOP riven with suspicions over his conservative credentials and with fears for its own political survival inside his Nov. 8 ballot blast zone. After a Friday meeting, House Republicans said sound bites distorted how personable Trump was. So why not show the good side if he really wants to win?

The New Yorker is well-known as a master media manipulator. Anytime a primary competitor had good news to tout, Trump created his own story to drown that out and dominate the news cycle. Quite skillful as such activities go.

But now that Clinton has serial setbacks, Trump routinely steps in to divert attention back to himself. Whether it’s his uncontrollable spotlight addiction or not, the result is to protect the Democrat he allegedly wants to defeat.

Thus Trump forfeits political opportunities to cash in on Clinton troubles. For instance, FBI Director James Comey gave Clinton a gift by declining to prosecute her for the email scandal. But the first 10 minutes of Comey’s on-camera remarks read like a federal indictment for perjury and national security violations.

Trump could also point out that Clinton’s emails were under subpoena when she destroyed them. A gold mine for a genuine opponent.

But no. Instead, Trump dredged up his old remarks about Saddam Hussein being a great terrorist-killer. And reignited attention to his Star of David gaffe by distributing a similar image on a Disney ad. Seriously? The media are evergreen Republican targets, but they’re not on the ballot.

Wealthy businessmen like longtime Democratic supporter Trump have run as political outsiders before. Remember former Democrat Wendell Willkie as the 1940 GOP nominee? Of course not.

More recently, another billionaire businessman named Ross Perot spent lavishly to challenge the Republican establishment and orthodoxy in a 1992 third-party bid that captured 19 percent of the popular vote.

The results of that populist effort served to split the GOP and — oh, look! — elect a Democrat named Clinton. Is it a coincidence that it’s happening again?

Andrew Malcolm is an author and veteran national and foreign correspondent.