Did President Trump's former campaign chairman collude with the Russians? AP correspondent Matt Small reports.

Deputy Attorney General Rod Rosenstein has empowered the Justice Department's special counsel to investigate allegations that President Donald Trump's former campaign chairman colluded with the Russian government.

That detail is revealed in a court document filed late Monday by special counsel Robert Mueller defending the scope of his investigation.

Paul Manafort, who led the Trump campaign for parts of 2016, has challenged Mueller's authority and asked a judge to dismiss an indictment against him.

But in its court filing, Mueller disclosed a memo from last August in which Rosenstein specified allegations that were within the scope of his investigation.

Among those is an allegation that Manafort colluded with Russian government officials to interfere in the 2016 presidential election.

None of the charges Manafort currently faces alleges coordination with the Kremlin.