A huge clue — doubly huge, in fact — has surfaced in the global mystery behind President Donald Trump’s bizarrely timed, effusively toned congratulatory call to Turkey’s now-stronger-than-ever strongman president, Recep Tayyip Erdogan.

It is a revelation that, when it comes to Turkey and Erdogan, Trump has a towering conflict of interest. And this time attention must be paid. Because Trump himself would be the first to concede our source is not just believable, but downright unimpeachable.

“I have a little conflict of interest because I have a major, major building in Istanbul,” then-presidential candidate Trump said in a Dec. 1, 2015, interview when asked if Turkey can be a reliable partner. “It’s a tremendously successful job. It’s called Trump Towers — two towers, instead of one. Not the usual one, it’s two.”

Today we don’t really know what, if anything, Erdogan or Turkey may have done to help Trump build or profit from his Turkish twin towers. But we do know Trump raced to telephone his congratulations to Erdogan Monday after a referendum expanding the Turkish leader’s powers, even as international observers were declaring the voting occurred “on an un-level playing field” that included a state of emergency that prohibited opposing campaigns and jailed would-be campaigners.

And we know that Trump succumbed to a burst of startling candor when his interviewer questioned Turkey’s and Erdogan’s trustworthiness in another context.

It needs to be noted here that Trump wasn’t being interviewed that day by one of my old-school news pals. He was a guest on the Sirius XM radio show hosted by Stephen Bannon, who was then running Breitbart News, the very rightwing and sometimes alt-right-wing website.

Bannon is, at this writing, still Trump’s White House counselor, though he has fallen from grace as Trump has fallen in polls.

On that day, Bannon’s show was pushing a hardline slant that cast Erdogan as a “middleman” who was “making money off ISIS oil” that was to be delivered to Vladimir Putin’s Russia, a setup that supposedly displeased Putin. So there was Trump, in the position of being pressed to choose between two of his favorite authoritarian strongmen, each having a fondness for being bloody-tough with opponents.

Bannon asked his future White House boss: “What do you do with Turkey? ... Is Turkey a reliable partner?”

Trump began by praising Erdogan. He said Turkey has “a strong leader.” Also: “Turkey has been a reliable partner.” But, he said, “Things are getting complicated.”

That’s when Trump confessed (but never really explained) his pro-Erdogan “conflict of interest.” He added: “I’ve gotten to know Turkey very well. ... They’re amazing people.”

Trump then began talking about Syria, a place loaded with conflict but in which Trump clearly had little interest.

Bannon got it about Trump’s discomfort and set about asking leading questions designed to help steer Trump back to his comfort zone themes. “Isn’t your selling point” that you’re a commander-in-chief and “a lot of these guys are munchkins?”

You bet. “I’ve been saying to you and everybody else for years attack the oil,” — and Trump was galloping. “... Attack it but keep it because I want to keep the oil. ... We’ve got nothing because we have stupid leadership. ... We have to hit the oil and hit the banks. ... And who knows more about the banks than Trump? Nobody!”

Bannon momentarily forgot himself and slipped into a journalistic follow-up: “When you say you have a conflict of interest,” he began, ending by asking how Trump would “stand up to Turkey?” But Trump was back on his game and ignored his future strategist’s question: “You don’t want to have World War III over what we’re talking about.” He of course attacked his opponents, adding: “I have a great temperament. ... I’m tougher than all of them put together — times ten! ... I will get Russia, I will get Turkey and we’ll all get along.”

The Breitbart website article about the interview omitted any mention of Trump confessing he’d had a conflict of interest over Turkey. The progressive magazine Mother Jones listened and reported it. But Trump’s base doesn’t dig Mother Jones. And the mainstream media mainly missed it.

So that’s how we wound up being led by a president who praises both Putin (the KGB alum whose cyberattacks helped Trump become president and whose opponents have died suddenly and strangely) and Erdogan (who survived a coup, jailed a reported 45,000 people, fired or suspended 130,000, and silenced media coverage of opponents). That helped Erdogan win his referendum by a bare 1.3 percent.

And that won Erdogan a call of congrats from the rich man whose name shines down today upon Istanbul from not one but two towers.

Martin Schram is a Tribune News Service columnist.