Emails obtained by CNN show the FBI agent at the center of a Capitol Hill storm played a key role in a controversial FBI decision that upended Hillary Clinton’s campaign just days before the 2016 election: the letter to Congress by then-FBI Director James Comey announcing the bureau was investigating newly discovered Clinton emails.

The new revelation about FBI agent Peter Strzok comes as Republicans accuse him of being sympathetic to Clinton while seeking to undermine Donald Trump during the heat of the 2016 campaign season.

Strzok, who co-wrote what appears to be the first draft that formed the basis of the letter Comey sent to Congress, also supported reopening the Clinton investigation once the emails were discovered on disgraced former Rep. Anthony Weiner’s laptop, according to a source familiar with Strzok’s thinking. The day after Strzok sent his draft to his colleagues, Comey released the letter to Congress, reigniting the email controversy in the final days of the campaign.