Two sources warned, however, that the information was not conclusive, according to CNN.
"A secret order authorized by the court that handles the Foreign Intelligence Surveillance Act (FISA) began after Manafort became the subject of an FBI investigation that began in 2014", per Evan Perez, Shimon Prokupecz and Pamela Brown.
After the 2014 warrant ended, it was renewed again until earlier this year, in order to allow the FBI to investigate ties between Trump campaign associates and suspected Russian operatives.More news: 'Get out!' Julia Louis-Dreyfus wins record 6th consecutive Emmy for 'Veep'
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"It is unusual for a prosecutor to seek a search warrant against someone who, like Mr. Manafort, had already put his lawyer in contact with the Justice Department", the Times reports.
Manafort is a key figure in Special Counsel Robert Mueller's investigation into Russia's involvement in the election. Or Trump Tower digital chatter might have shown up while authorities dug through the vast quantities of data hoovered up via more sweeping foreign surveillance programs.
The unusual pace and aggression with which Mueller is moving against Manafort is a classic sign that the special counsel wants to coerce Manafort's cooperation in the Russian Federation probe, wrote former federal prosecutor Renato Mariotti. "The FBI interest deepened last fall because of intercepted communications between Manafort and suspected Russian operatives, and among the Russians themselves, that reignited their interest in Manafort", CNN reports. Nine months later, NBC News reported that Manfort himself was a focus of the FBI's probe into possible Russian interference in the 2016 election, an investigation that's since been taken over by former FBI Director Robert Mueller.
Mueller's focus on Manafort could be an attempt to "flip" him against Trump.
The president can complain all he wants about investigations of his associates.
"They seem to be pursuing this more aggressively, taking a much harder line, than you'd expect to see in a typical white collar case", Jimmy Gurulé, a Notre Dame law professor and former federal prosecutor, told the Times. Federal agents had raided Manafort's Virginia house in July.