A top lieutenant to Special Counsel Robert Mueller in his investigation into the Trump campaign's possible ties to Russia expressed his opposition to an early policy priority of President Donald Trump's by praising then-acting Attorney General Sally Yates for refusing to enforce Trump’s travel ban.

Andrew Weissmann served as the chief of the Justice Department's Criminal Fraud Section earlier this year and went on to become a top investigator on Mueller's team of prosecutors.

Weissmann sent an email in January, when he was still in his criminal fraud section role, to former acting Attorney General Sally Yates applauding her for her refusal to enforce Trump's temporary travel ban on people entering the United States from several predominantly Muslim countries.

"I am so proud. And in awe," Weissmann emailed Yates. "Thank you so much. All my deepest respects."

Earlier that day, Trump had fired Yates after she refused to defend the travel ban.

Weissmann's email is just one of several sent to Yates by DOJ officials praising her for defying Trump on the travel ban. Judicial Watch obtained the emails through a Freedom of Information Act lawsuit.

Judicial Watch President Tom Fitton said the findings clearly demonstrate Weissmann's anti-Trump bias and said the Mueller investigation has been "irredeemably compromised."

A New York Times article published in October described Weissmann as Mueller’s "pitbull" and said colleagues call him "relentless and uncompromising"; his critics said his "scorched-earth tactics" have sometimes backfired. Weismann also oversaw the pre-dawn raid of former Trump campaign aide Paul Manafort, according to the report.

"This is an astonishing and disturbing find," Fitton said Tuesday. "Andrew Weissmann, a key prosecutor on Robert Mueller’s team, praised Obama DOJ holdover Sally Yates after she lawlessly thwarted President Trump. How much evidence do we need that the Mueller operation has been irredeemable compromised by anti-Trump partisans? Shut it down."

The new email revelations showing strong, early bias by Justice Department employees against Trump's travel ban comes amid new scrutiny of the FBI probe into Hillary Clinton's emails and on Mueller's investigative team.

House Intelligence Committee Chairman Devin Nunes over the weekend directed his staff to prepare a contempt of Congress resolution against FBI Director Christopher Wray and Deputy Attorney General Rod Rosenstein for any role they might have played in "hiding" a top agent's alleged bias against Trump

Nunes threated to hold the DOJ official in contempt of Congress for failing to disclose the reasons behind the removal of FBI agent Peter Strzok from Mueller's investigative team. Strzok was removed from the special counsel's probe after the Justice Department uncovered work emails from Strzok to another FBI agent that appear to criticize Trump.

Judicial Watch's FOIA lawsuit produced other emails, all from Justice Department email addresses, expressing strong support for Yates's decision.

Liz Aloi, who was serving as chief of the Justice Department's special financial investigations unit, said Yates was "inspirational and heroic." She remains the chief of the unit, according to her LinkedIn page.

Jeffrey Clair, a Justice Department Civil Division Appellate Attorney, thanked Yates and wrote: "I've been in civil/appellate for 30 years and have never seen an administration with such contempt for democratic values and the rule of law."

"The president's order is an unconstitutional embarrassment and I applaud you for taking a principled stand against defending it," he added.

It is unclear if Clair is still working at the Justice Department. The DOJ did not immediately respond to a request for comment.

The U.S Supreme Court on Monday allowed the latest version of Trump's travel ban to take effecting pending an appeal.

The Trump administration modified the travel ban two times in response to lower court decisions to block it, with the administration’s latest version coming out in September. It places new limits on travel to the U.S. by foreign nationals from eight countries: Chad, Iran, Libya, North Korea, Syria, Venezuela, Somalia, and Yemen.

Several U.S. attorneys also sent emails to Yates, lauding her for her defiance to Trump on the travel ban. Trump in early March dismissed all U.S. attorneys appointed by President Barack Obama.

Thomas Delahanty, who was serving as U.S. attorney for Maine, appointed by Obama, wrote to Yates: "You are my hero."

Emily Gray Rice, then the U.S. attorney for New Hampshire appointed Obama, said: "AAG Yates, thank you, as always, for making us proud. It is truly an honor to work for you."

Another Obama appointee, Barbara McQuade, who was serving as the U.S. attorney for the Eastern District of Michigan, said: "Thank you for your courage and leadership. This is wonderful news."