The CNN report suggests that US investigators obtained the FISA warrant after the now-infamous June 9, 2016 Trump Tower meeting between Manafort, Donald Trump Jr., Jared Kushner and a group of Russian lobbyists.
According to CNN, investigators picked up communications from Manafort which suggested that he might have encouraged Russian operatives to meddle in the campaign.
CNN added that two of its three unnamed sources admitted that their "evidence is not conclusive". Although that surveillance ceased in 2016, the FBI resumed it until at least early in 2017 due to the bureau's concern about suspected collusion between individuals tied to the Trump campaign and individuals believed to be Russian operatives.
Warrants issued by the court established by the Foreign Intelligence Surveillance Act are based on probable cause that a person is an agent of a foreign power.
And let's not forget, Manafort became Trump's campaign manager in June 2016 but was forced to resign two months later amid reports of his business relationship with the Kremlin-backed former Ukrainian leader, Viktor Yanukovich.
It does not seem that Manafort was wiretapped while he served as Trump's campaign chairman.
Meanwhile, Hillary Clinton, who lost the election to Mr Trump, said Monday that she "wouldn't rule out" questioning the legitimacy of the presidential election if evidence emerged of Russian interference.
"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. "The special counsel even took the unusual step of obtaining a subpoena for one of Mr. Manafort's former lawyers, claiming an exception to the rule that shields attorney-client discussions from scrutiny".
While Manafort keeps a residence at Trump Tower, there is still no evidence Trump himself was under surveillance.
CNN has learned U.S. authorities wiretapped Paul Manafort, the spin artist for dictators who worked a tumultuous four-and-a-half month term as Donald Trump's campaign manager in 2016.
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. Several sources close to the president, including veterans of the campaign, told The Daily Caller early in September that they expect Manafort will be indicted for financial crimes like money-laundering or tax evasion.