FBI Special Counsel Robert Mueller’s top deputy attended Hillary Clinton’s election night party in New York City, according to a report released Friday.

The Wall Street Journal reports Andrew Weissmann, a top FBI attorney also referred to by the New York Times as Mueller’s “pit bull,” attended former 2016 Democratic presidential nominee Hillary Clinton’s election night soiree, fueling concerns that he and others on Mueller’s team may have an anti-Trump bias.

Election filings show that Weissmann donated several thousand dollars to the Democratic Party. Records show Weissmann donated $2,350 to the Obama Victory Fund in 2008, and contributed $2,000 to the DNC in 2006.

Former White House Press Secretary Ari Fleischer, who served under former President George W. Bush, tweeted Saturday that Weissmann should be “disqualified” from the investigation into President Trump’s campaign because of his open support for Clinton as a candidate.

There are 2 reasons people attend a candidate’s victory party. 1) They’re cheering for the candidate to win. 2) They want a job/promotion if the candidate wins. Both reasons should disqualify Weissmann from investigating Trump. https://t.co/Zffzobbo6j — Ari Fleischer (@AriFleischer) December 9, 2017

The report about Weissmann’s attendance is the latest blow to the top attorney’s credibility, as well as the credibility of Mueller’s Russia probe as a whole.

Conservative watchdog Judicial Watch exposed another instance of Weissmann’s anti-Trump bias after publishing an email exchange between Weissmann and then-acting Attorney General Sally Yates’showing Weissmann gushing about Yates’s decision not to enforce Trump’s travel ban in January.

“I am so proud. And in awe. Thank you so much. All my deepest respects,” Weissmann wrote Yates in an email obtained by Judicial Watch in a Freedom of Information Act lawsuit.

Mueller’s probe is under increased scrutiny, especially after it was revealed that Mueller fired FBI counterintelligence investigator Peter Strzok over anti-Trump text messages he exchanged with an FBI attorney he reportedly had an affair with.

Two investigators on Mueller’s team have also done past legal work for people tied to Clinton, adding more fuel to claims of bias within the investigation.

Aaron Zebley, Mueller’s former chief-of-staff when the special prosecutor was FBI director, represented Justin Cooper, the Clinton aide responsible for destroying Hillary Clinton’s email server.

Jeannie Rhee, another lawyer Mueller chose to serve on the investigation, represented the Clinton Foundation, Hillary Clinton herself, and former Obama Deputy National Security Adviser Ben Rhodes.

Rhee and Weissmann both worked together at the white-shoe law firm WilmerHale before being asked to serve on the Russia investigation.