A former CIA chief of staff slammed Fox News for an absolutely despicable attack on a decorated combat veteran who is set to testify on Tuesday in the impeachment inquiry against President Donald Trump .

Army Lt. Col. Alexander Vindman, the top Ukraine expert on the National Security Council, will reportedly tell lawmakers that he heard Trump pressure Ukrainian President Volodymyr Zelensky into digging up dirt on former Vice President Joe Biden and son Hunter Biden.

Vindman, who listened in on the July 25 call between Trump and Zelensky, is set to testify that he twice reported the incident to a superior, according to an opening statement obtained by The New York Times .

Vindman received a Purple Heart after an injury from a roadside bomb and remains an active-duty officer.

But people on Fox News are already questioning his loyalty and patriotism. Laura Ingraham noted the Times story reported that Vindman emigrated to the U.S. from Ukraine as a child and that Ukrainian officials asked him in English for advice on dealing with Trump attorney Rudy Giuliani. She then accused Vindman of working apparently against the presidents interests while inside the White House.

Isnt that kind of an interesting angle on the story? the conservative personality asked guest John Yoo, the former Justice Department lawyer who helped write the infamous torture memos during the George W. Bush presidency.

Yoo said it went far beyond interesting.

I find that astounding, he said. Some people might call that espionage.

MSNBC s Brian Williams described the Fox News attack as an opening salvo in character assassination on Vindman. His guest, former CIA chief of staff Jeremy Bash, agreed.

I think theyre alleging a U.S. Army colonel is a traitor, Bash said, adding:

Here we have the followers of Donald Trump doing what I think is absolutely despicable, which is claiming that not only is he against Trump but hes un-American and I dont think Republicans , Democrats , anybody who cares about our country, are going to stand for that.

See his full discussion with Williams above.