As it turns out, special counsel Robert Mueller has been investigating Donald Trump’s former campaign manager Paul Manafort for “collusion” for months.

Manafort has already been charged with a slew of financial crimes, including money laundering and tax fraud, as a result of the Russia probe. But he’s been trying to get those charges dismissed by arguing that they’re outside of Mueller’s mandate to investigate alleged collusion between the Russian government and the Trump campaign. Deputy Attorney General Rod Rosenstein, however, gave Mueller broad authority to investigate both Manafort’s career in foreign lobbying and alleged collusion eight months ago, a memo released Tuesday night revealed.

That authority could make Manafort’s attempts to wriggle out of his charges more difficult.

“It was always going to be a difficult argument to make that Mr. Mueller exceeded his legal mandate with the charges brought against Mr. Manafort, but this may well put the issue to bed,” said Josh Rosenstein, partner at Sandler Reiff, a Washington, D.C.-based political law form, and an expert in foreign lobbying regulation.

So far, none of the charges against Manafort, which are being heard in two different courts, have been linked to Russian meddling in the 2016 U.S. election. They’re largely financial crimes related to his work on behalf of foreign governments, including a pro-Russian Ukrainian political party. Critics on the right like to point to that fact. They’ve even called the financial lobbying charges against Manafort “mission creep.”

Since his charges first came down in October, Manafort has asked the D.C. federal court to dismiss them on the basis that Mueller has no right to charge him with crimes unrelated to his work as Trump campaign manager in 2016.

But the memo indicates Russian collusion has been at the center of the investigation into Manafort for awhile; Russian-related charges against Manafort could even be coming.

The memo, which Rod Rosenstein sent to Mueller in August 2017, confirms that the Justice Department has long had reason to believe Manafort may have colluded with Russia. Rod Rosenstein’s original May 2017 order instructing Mueller to investigate “any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump” did not name specific campaign individuals under investigation. But the memo — a follow-up on that original order — specifically names Manafort as a campaign member who may have colluded with the Russians. It also specifically authorizes Mueller to investigate payments Manafort received from the Ukrainian politicians, which led to the financial charges already brought against him.

Federal judge Amy Berman Jackson, an Obama appointee, will decide if the D.C. case against Manafort can go forward. Manafort also faces charges from the special counsel, including bank fraud and tax evasion, in Virginia federal court. He’s trying to get that case dismissed as well.

President Donald Trump has tweeted more than 20 times that there was “no collusion” between his campaign and Russia. He’s even criticized Rosenstein in the past for being “a Democrat.” (He’s a Republican.) A Trump adviser told the Washington Post in 2017 that Trump viewed Rosenstein as a threat to his presidency.

The memo could bring more heat from the president down on Rosenstein. By giving Mueller authority to dig into Manafort’s alleged collusion with Russia, Rosenstein allowed Mueller to take the investigation closer to the president himself.

Read Rod Rosenstein's full memo here: