Donald Trump has tapped Citizens United president David Bossie, a man with two decades of research into Hillary and Bill Clinton under his belt, to serve as his deputy campaign manager.

Bossie has known Trump for years, and has advised him informally. But his secret weapons may be an untapped reservoir of dirt on the Democratic nominee for president, an instant recall of opposition research and strategic instincts about how to deploy it.

He once led the research team behind the House Oversight and Government Reform Committee when it dug into Bill Clinton's past as part of a wide-ranging 1990s investigation of the Whitewater land-deal scandal.

OLD PALS: Donald Trump has hired David Bossie (right), president of Citizens United, as deputy campaign manager. The two are pictured onstage at the May 2015 South Carolina Freedom Summit, which Bossie co-hosted

DEEP-DIVE: Bossie brings with him more than 20 years of Clinton research and a history of political strategy that Trumpworld hopes will be a difference-maker

Citizens United spokesman Bryan Lanza took a job with the Trump campaign in mid-July connecting reporters with political and policy experts who support the billionaire's candidacy.

Trump told the Post that Bossie, who introduced him to his first campaign manager Corey Lewandowski in early 2015 – and this year to current campaign chairman Steve Bannon – has been 'a friend of mine for many years.'

'Solid. Smart. Loves politics, knows how to win.'

Bossie also organized a key Republican 'Freedom Summit' cattle-call in May 2015 as Trump was weighing a formal dive into the race. The South Carolina event helped establish the billionaire as more than a flavor-of-the-week novelty.

Campaign manager Kellyanne Conway added that Bossie, tasked to help with strategic planning and day-to-day operations, is 'a battle-tested warrior and a brilliant strategist' and 'a nuts-and-bolts tactician as well, who's going to help us fully integrate our ground game and data operations.'

NUMBER TWO: Bossie will back up pollster Kellyanne Conway, Trump's campaign manager

The Citizens United organization is best known for bringing the landmark 2010 Supreme Court case that established political donations as a form of constitutionally protected free speech.

The fallout from the case has empowered corporations, unions and wealthy Americans to donate unlimited amounts of money to so-called 'super PACs' that support candidates but can't legally collaborate with them.

Until this week Bossie himself was running an anti-Clinton super PAC named 'Defeat Crooked Hillary.'

And his Citizens United has been one of the most aggressive groups behind Freedom of Information Act cases aimed at prying Clinton-related emails and other documents from the U.S. State Department.

Much of the recent news cycles focused on the potentially criminal overlap between Clinton's role as secretary of state and a steady flow of foreign cash into her family foundation has come at Bossie's urging.

CONNECTIVE TISSUE: Bossie is seen as a relationship broker in the conservative movement, and introduced Trump to both current campaign CEO Steve Bannon and former campaign manager Corey Lewandowski (pictured)

His place in history has its roots in a 2008 film, 'Hillary: The Movie,' which he produced as Clinton was deep in her first run for the White House.

When t he Federal Election Commission labeled it a form of 'electioneering' and prohibited the nonprofit and tax-exempt Citizens United from buying TV airtime to advertise or show it in the months before the election, the group sued on First Amendment grounds.

Clinton complained last year in an interview with the Associated Press that the Supreme Court ruling should be overturned.

'They took aim at me, but they ended up damaging our entire democracy,' she said then.