A lawyer for Lt. Col. Alexander Vindman sent a letter to Fox News Wednesday requesting the network retract a segment alleging that Vindman, who was born in Ukraine and is fluent in Russian and Ukrainian, committed "espionage."

Catch up quick: Fox News' Laura Ingraham questioned Vindman's role as the National Security Council’s Ukraine expert in a segment of her show on Oct. 29, stating, “Here we have a U.S. national security official who is advising Ukraine, while working inside the White House, apparently against the president’s interest, and usually, they spoke in English. Isn’t that kind of an interesting angle on this story?”

George W. Bush administration lawyer John Yoo, a guest on the show, responded: "I found that astounding. Some people might call that espionage."

The network has failed to correct the allegation. Espionage is a felony punishable by death.

Between the lines: The letter comes one day after Vindman publicly testified to Congress as part of an impeachment inquiry into President Trump. Vindman testified that he found the July 25 phone call between Trump and Ukrainian President Zelensky to be "improper," and that he reported it to a White House lawyer.

GOP counsel Steve Castor asked Vindman at length about an offer to become Ukraine's defense minister, which Vindman called "rather comical." Vindman has faced unsubstantiated cable news attacks from Fox News questioning his loyalty to the U.S. because he was born in Ukraine.

What they're saying: The letter states that prior to Fox News' report, Vindman had "never in his decorated 20-year career of service to his country been accused of having dual loyalties or committing espionage."

"Fox News has a responsibility to help put out the fire it lit when it falsely accused a decorated soldier of disloyalty to his country. LTC Vindman, who has dedicated his life to defending America out of the public eye, deserved better than to be falsely attacked when compelled by law and duty to speak the truth."

Fox News has responded: "As a guest on FOX News, John Yoo was responsible for his own sentiments and he has subsequently done interviews to clarify what he meant."

Read the letter

Go deeper: