Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. His new book is "Trump and His Generals: The Cost of Chaos." The opinions expressed in this commentary are his own. View more opinion articles at CNN.

(CNN) Retired Marine Gen. John Kelly said at an event at Drew University on Wednesday that Lt. Col. Alexander Vindman did the right thing when he raised concerns about President Donald Trump's call to the Ukrainian president in late July, according to a report in The Atlantic.

Peter Bergen

Kelly said that when Vindman heard Trump telling Ukrainian President Volodymyr Zelensky that he wanted investigations into former Vice President Joe Biden and his son, Hunter, he was guided by what the US military teaches -- that you report to your superiors actions which you believe to be wrong.

The Atlantic reported that Kelly explained, "We teach them, 'Don't follow an illegal order. And if you're ever given one, you'll raise it to whoever gives it to you that this is an illegal order, and then tell your boss.'"

We have come to an extraordinary moment in the United States when some of the most senior retired military leaders in the country are publicly taking President Trump to task. Traditionally, such officers have not taken political positions, even in retirement. And now Kelly, who was Trump's chief of staff in the White House -- historically the cabinet official who spends the most time with the president -- is one of those public critics.

While Kelly's comments are the most wide-ranging public critique of the President and his policies by any of the generals who served in cabinet posts in the Trump administration, others have also spoken out.

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