WATCH: Alexander Vindman explains how Donald Trump Jr. violated the Ku Klux Klan Act
Donald Trump, Jr. (screengrab)

Lt. Col. Alexander Vindman (U.S. Army, retired) explained on CNN on Thursday why he is suing Donald Trump, Jr., Rudy Giuliani, former White House deputy chief of staff Dan Scavino, and former White House deputy communications director Julia Hahn.

"Can you tell us, colonel, why you are filing this?" CNN's Brianna Keilar asked.

"Sure," Vindman replied. "I think this is a critically important effort to hold accountable corrupt officials, close relatives, and inner circle for Donald Trump in their effort to stifle the duties of an official in the U.S. government. This had enormous chilling effect on both the folks that would come forward to report wrongdoing in that administration but also intended to suppress officials in the conduct of their duties. To this day we see folks being too scared to come forward, too scared to come out and speak up against the corruption they're witnessing."

"So Donald Trump, Jr., for example, what specifically did he do that crossed the line, that was in violation of the Ku Klux Klan act, as you allege?" Keilar asked.

"There's wide reporting about Donald Trump, Jr. being a surrogate for his father," Vindman replied. "When his father couldn't speak out publicly — and his father did often speak out publicly — Donald Trump, Jr. would speak out and attack witnesses, attempt to impugn folks' character, and really just drive up the level of hate and rhetoric around officials that went against the -- proceeded to go against Donald Trump, even though Donald Trump was the one that was the corrupt actor."

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"That is why I'm bringing the suit, there must be accountability against these actors, and Donald Trump couldn't do this without the support of his subordinates," he added.