Then-national security adviser Michael Flynn and President Trump arrive at MacDill Air Force Base in Tampa on Feb. 6, 2017. (Mandel Ngan/AFP/Getty Images)

Jon Iadonisi, a friend and business associate of former national security adviser Michael Flynn, had two under-the-radar projects underway in the fall of 2016.

One of his companies was helping Flynn with an investigative effort for an ally of the Turkish government — details of which Flynn revealed only after he was forced to step down from his White House post.

At the same time, Iadonisi was also doing work for the Trump campaign, although his role was not publicly reported, according to people familiar with his involvement.

The project Iadonisi was engaged in for Trump’s campaign focused on social media, according to a person with knowledge of the arrangement. What that work consisted of — and why his company was not disclosed as a vendor in campaign finance reports — remains a mystery.

The Trump campaign did not report any payments to Iadonisi or his firms. However, Federal Election Commission reports show that the Trump campaign paid $200,000 on Dec. 5 for “data management services” to Colt Ventures, a Dallas-based venture-capital firm that is an investor in VizSense, a social-media company co-founded by Iadonisi.

The Washington Post made repeated inquiries to Iadonisi and other VizSense officials, but none responded to requests for comment.

Michael Glassner, executive director of the Trump campaign committee, said invoices show Colt Ventures was paid for a ­social-media project that involved video-content creation and “millennial engagement” in the campaign’s final month. He declined to comment on why the payment went to a venture-capital firm and whether campaign officials were aware of the firm’s connection to VizSense and Iadonisi.

It is common for political vendors to hire subcontractors whose work is not publicly reported. However, campaign committees cannot seek to avoid disclosure by paying an entity that does not have a legitimate relationship with the ultimate recipient, said Washington campaign-finance lawyer Daniel Petalas, who served as the FEC’s acting general counsel and head of enforcement.

“A venture-capital company is certainly a strange entity for a campaign to be making an expenditure to, and I would want to look further to assess whether it was it an appropriate recipient,” he said.

Colt Ventures was founded by Darren Blanton, a Dallas investor who later served as an adviser to Trump’s transition. Blanton met frequently with Trump strategist Stephen K. Bannon at Trump Tower during the campaign, according to people who saw him there. Colt also sent a report to Bannon about work done for the campaign, according to a person familiar with the matter.

It is unclear who approved the contract with Colt Ventures. Bannon declined to comment, but a White House official said Bannon is “not aware of any of these companies or contracts.”

Blanton did not respond to requests for comment. However, shortly after the The Post first contacted him, Colt Ventures updated an online list of companies that make up its investment portfolio and added VizSense.

VizSense, based in Plano, Tex., promises on its website to “weaponize your brand’s influence” through “military-grade influencer marketing and intelligence services.”

Iadonisi, a former Navy SEAL, started the company in 2015 with Tim Newberry, a nuclear engineer who served as a submarine officer. It was spun out of the duo’s consulting firm, White Canvas Group, which they once described as a “a privatized DARPA,” a reference to the Pentagon’s research arm.

White Canvas has received numerous Pentagon contracts, including nearly $150,000 last year from the Navy for “deep and dark web capability and gap analysis,” according to contracting records.

In a 2015 interview with the Dallas Morning News, Iadonisi said VizSense helps clients track online video performance and identify which social-media users drive the most traffic. He said he witnessed the power of viral media firsthand while serving in Iraq.

“We know of a lot of bad guys who were killing my friends, and they were really good at making viral videos,” Iadonisi said. “These videos catalyze, and now we can look at data.”

Iadonisi, who worked with the CIA as a Navy SEAL, according to an online biography, has close ties to Flynn, a retired Army lieutenant general with whom he served in Iraq. His LinkedIn page features an endorsement from Flynn, who called Iadonisi “one of the best problem solvers I have ever worked with” and “an incredible asset for any organization.”

In late December, the official VizSense account tweeted praise of Flynn, writing that he “is going to construct an NSC that is custom built for what America needs to be first!@DanScavino @GenFlynn @realDonaldTrump.”

Flynn declined to comment through his attorney. But a person with knowledge of their relationship said Flynn has no stake in Iadonisi’s companies and received no financial benefit from any of Iadonisi’s campaign work.

Until recently, Iadonisi and Flynn’s firms shared an office suite in Alexandria, Va. Flynn’s now-closed consultancy, Flynn Intel Group, rented space from White Canvas Group, according to a person familiar with the arrangement.

And last fall, Flynn tapped White Canvas Group to help him investigate Fethullah Gulen, a Turkish Islamic cleric who lives in Pennsylvania, Justice Department documents show.

The research was financed by a company owned by Ekim Alptekin, a Turkish American businessman close to top officials in Turkey, the documents show. Turkey’s president, Recep Tayyip Erdogan, accuses Gulen of fomenting a coup attempt last summer and wants him extradited from the United States.

Inovo, a Netherlands-based company owned by Alptekin, paid Flynn Intel Group $530,000 to activate an “investigative laboratory” made up of former top security and intelligence officials to research Gulen, according to documents Flynn filed under the Foreign Agents Registration Act. Flynn, in turn, paid White Canvas Group $15,000 for “public open source research,” according to disclosures.

In its contract with Inovo, Flynn Intel Group said the Gulen investigation would be done by “its most senior principals,” including “the head of Flynn Intel Group’s Special Operations Cyber Force.”

At the time, that role appeared to be filled by Newberry, Iadonisi’s partner and the chief executive of White Canvas Group.

In August 2016, the same month the Inovo contract was signed, Newberry temporarily took on an additional post: chief executive of FIG Cyber, a unit of Flynn Intel Group, according to his LinkedIn profile. He held the title until November, when the Inovo contract ended. Newberry did not respond to requests for comment.

Flynn stepped down as national security adviser in February after misleading administration officials about his contacts with the Russian ambassador. He retroactively registered as a paid foreign agent for Turkish interests in March in disclosures to the Justice Department.

The Defense Department’s inspector general is investigating payments Flynn received from Inovo and other foreign groups. Defense Department guidelines require former officers to obtain permission before working for foreign governments.

Steven Rich contributed to this report.