President Donald Trump has named Brad Parscale to be his 2020 campaign manager.

On Tuesday morning, Trump released a statement calling Parscale a “longtime digital marketing strategist for President Trump” who was “essential in bringing a disciplined technology and data-driven approach to how the 2016 campaign was run.”

Trump is not being hyperbolic here: Parscale, who was in charge of the Trump campaign’s digital operations and worked closely with Facebook, Twitter, and Google to hone the campaign’s social media presence, was a huge part of why Trump won the White House. A 2017 profile on 60 Minutes called Parscale the “secret weapon” of Trump’s social media strategy.

“I understood very early that Facebook was how Trump was going to win,” Parscale said of the campaign’s use of social media during the 2016 presidential campaign. “I think we used it better than anyone ever had in history.”

But the young tech guru who ran the Trump campaign’s digital operations from his office in San Antonio is an extremely controversial choice to run the president’s 2020 campaign — particularly given that Trump’s 2016 campaign is still being investigated for potential collusion with Russia.

That’s because Parscale is intimately tied to a company called Cambridge Analytica, a shady data analytics firm that has become a major focus of both the House Intelligence Committee’s investigation into Russian meddling in the election and special counsel Robert Mueller’s probe.

Here’s what you need to know.

The Cambridge Analytica connection

Cambridge Analytica is a data company that specializes in what’s called “psychographic” polling, which means it uses data collected online to create personality profiles for voters. It then uses that information to target individuals with content tailored to their specific profile.

Last December, Mueller requested that Cambridge Analytica turn over internal documents as part of his investigation into possible collusion between the Trump campaign and Russia during the 2016 election.

The thread connecting Russia, the Trump campaign, and Cambridge Analytica is Michael Flynn, Trump’s former national security adviser who was forced to resign after he reportedly lied to Vice President Mike Pence and the FBI about his phone conversations with a Russian envoy in 2016.

A series of reports last July by the Wall Street Journal’s Shane Harris, Michael Bender, and Peter Nicholas revealed that Peter Smith, a pro-Trump GOP operative, sought to acquire 30,000 deleted emails from Hillary Clinton’s private server. Two of the groups Smith reached out to had connections to Russia.

Smith told Harris that he was in regular contact with Flynn, who at the time was still working closely with Trump’s campaign. Harris also reported on intelligence assessments that outlined the efforts of Russian hackers to retrieve Clinton’s emails and pass them on to Flynn, who would then share them with the Trump campaign.

Via an August 2017 Associated Press report, we also know that Flynn was later forced to disclose “a brief advisory role with a firm related to a controversial data analysis company that aided the Trump campaign.”

That “data analysis” company was Cambridge Analytica.

We don’t know what data Flynn might have shared with the Russians (or vice versa). Nor do we know if — or to what extent — the Trump campaign coordinated with the Russians to help their disinformation operation.

What we do know is that Russia was actively meddling in the 2016 presidential election in order to help Trump win the White House. We also know that part of its operation relied on manipulating Facebook’s algorithms to target specific voters.

And this is precisely the sort of work that Cambridge Analytica and Brad Parscale were hired to perform for the Trump campaign.

How does Parscale figure into all this?

Jared Kushner hired Cambridge Analytica to take over the Trump campaign’s data operations in 2016. Kushner also hired Parscale to develop the campaign’s online microtargeting strategy.

According to the New York Times’s Nicholas Confessore and Danny Hakim, Cambridge Analytica convinced Parscale to “try out the firm.” The decision was encouraged by Trump’s campaign manager at the time, Steve Bannon, who was also a former vice president of Cambridge Analytica.

We don’t know how instrumental Cambridge was to Parscale’s online strategy, but it seems reasonable to assume that it was important. Although Parscale denied during his 60 Minutes interview that the firm was useful, we know that the campaign’s digital operation was extraordinarily effective.

The Guardian’s Carole Cadwalladr reported that Trump’s campaign “was using 40-50,000 variants of ads every day that were continuously measuring responses and then adapting and evolving based on that response.” These ads were spread primarily through bots on social media platforms.

During that same 60 Minutes interview, Parscale insisted that allegations of collusion between the Trump campaign and Russia were “a joke.” But there’s a mountain of circumstantial evidence that suggests otherwise, and if it turns out that the Trump campaign did help Russia target voters, we’ll likely hear more about Cambridge Analytica and Parscale’s role.

It may turn out that Parscale did nothing wrong and had no connections to Russia’s disinformation campaign. But his proximity to all of this makes him an unusual choice to lead Trump’s 2020 reelection campaign.