Washington (CNN) One of the aspects of "possible political bias" mentioned --and then dismissed -- in the Intelligence Community Inspector General report refers to the fact that the anonymous whistleblower who filed a complaint about President Donald Trump's interactions with the Ukrainian President is a registered Democrat, a source familiar with the ongoing investigation told CNN Thursday.

The intelligence community's inspector general, Michael Atkinson, acknowledged an indication of possible political bias in his assessment of the complaint but made clear that it did not change his overall conclusion that it appeared to be credible.

"Further although the ICIG's preliminary reviewed identified some indicia of bias of an arguable political bias on the part of the complainant in favor of a rival political candidate, such evidence did not change my determination that the complaint relating to the urgent concern 'appears credible' particularly given the other information the ICIG obtained during its preliminary review," Atkinson wrote.

Mark Zaid, an attorney for the whistleblower, responded to this story on Twitter by saying, "We won't comment on identifying info but if true, give me a break! Bias? Seriously? Most ppl are."

A week after the source spoke to CNN, Zaid and Andrew Bakaj, another attorney for the whistleblower, acknowledged that the indicia could possibly also include that the whistleblower as a government employee came "into contact with presidential candidates from both parties in their roles as elected officials -- not as candidates." They said that the whistleblower "has never worked for or advised a political candidate, campaign or party."

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