Carter Page, a foreign policy adviser to during President Trump's campaign, has been the subject of a foreign surveillance warrant since 2014.

It was previously reported that Page had been under surveillance since last summer, after he left the campaign.

Page, as well as former campaign chairman Paul Manafort, former national security adviser Mike Flynn, and Trump confidant Roger Stone had been the focus of the Russia investigation even before special counsel Robert Mueller was appointed, according to a CNN report. Mueller has reportedly issued grand jury subpoenas related to the June 2016 meeting Jared Kushner, Donald Trump Jr., and Manafort.

It was previously reported that Page had been under surveillance since last summer, after he left the campaign.

The FBI has questioned him numerous times this year. Page said he cooperated and agreed to be interviewed without his lawyer present.

Page has long been the subject of federal investigators throughout the Russia investigation amid allegations he either worked as an agent of a foreign government or colluded with one. He runs a New York consulting firm that has done business with Russia.

In recent months, Page has complained that he is willing to testify before the committees doing Russia investigations, but told the Washington Examiner that he's been "completely blocked" from doing so.