Paul Manafort, former campaign manager for U.S. President Donald Trump arrives for a bond hearing at U.S. District Court in Washington, U.S., November 6, 2017. REUTERS/Joshua Roberts - RC18AD95AAE0

WASHINGTON (AP) — Deputy Attorney General Rod Rosenstein explicitly authorized the Justice Department’s special counsel to investigate allegations that President Donald Trump’s former campaign chairman colluded with the Russian government, according to a court filing.

Special counsel Robert Mueller’s team of prosecutors included that detail in a memo defending the scope of their investigation, which so far has resulted in criminal charges against 19 people and three Russian companies.

Paul Manafort, who led Trump’s Republican campaign for several months in 2016, has challenged Mueller’s authority and asked a judge to dismiss an indictment charging him with crimes including money laundering conspiracy and false statements. He said Mueller, who was assigned to investigate potential coordination between Russia and the Trump campaign, overstepped his bounds by charging him for conduct that occurred years before the 2016 presidential election.

But in their new filing late Monday, prosecutors revealed that Rosenstein — who appointed Mueller — wrote a memo last August that outlined the scope of Mueller’s appointment.

The memo, which had not previously been…