Before dawn on July 26, agents showed up at Manafort's home without warning, presented a search warrant, and gathered many documents, per Post reporters Carol Leonnig, Tom Hamburger, and Rosalind Helderman.
Law enforcement authorities seeking to obtain a search warrant must generally establish to a judge that there is probable cause to believe that a crime may have been committed.
Manafort had previously given documents voluntarily to the congressional committees investigating the Russian election meddling.
Last August, The New York Times discovered that a pro-Russian political party in Ukraine designated $US12.7 million in undisclosed cash payments for Manafort, who had advised the party and its former leader, Viktor Yanukovych, for almost a decade.
Manafort led the Trump campaign for several months. News reported that a Manafort spokesman had confirmed the raid occurred.
Since May, Mueller has amassed "three dozen attorneys, investigators and other staff in a nondescript office in Washington", CNN reports.
Trump vows to 'win' opioid crisis fight, doesn't declare emergency
The panel also suggested Trump "declare a national emergency under either the Public Health Service Act or the Stafford Act". He might also be able to direct more public health personnel toward states overwhelmed by the epidemic.
In recent days, it has become clear the former Federal Bureau of Investigation director is using a grand jury in Washington in addition to one in the Eastern District of Virginia, where investigators have also been looking into Mr Trump's former national security adviser Michael Flynn.
Fusion GPS, the firm that compiled a dossier at the center of the federal Russian Federation probe, has not yet turned over any documents, according to the committee's spokesperson, though a source told CNN the firm plans to provide the committee with "thousands" of pages of documents Wednesday.
Mr Manafort left the Trump campaign over questions about his foreign ties.
On the day of the raid, President Trump tweeted, "Why didn't A.G. Sessions replace Acting FBI Director Andrew McCabe, a Comey friend who was in charge of Clinton investigation but got big dollars ($700,000) for his wife's political run from Hillary Clinton and her representatives".
The search was carried out shortly after Mr. Manafort met with investigators for the Senate Intelligence Committee on July 25.
Donald Trump's presidential campaign has turned over more than 20,000 pages of documents the Senate Judiciary Committee requested concerning the campaign's attempts to receive information about Hillary Clinton from Russian Federation and affiliated sources, Bloomberg News reported.