Washington (CNN) Former national security adviser John Bolton, who has been a central figure in Democrats' fight to hear from witnesses in the Senate trial, defended on Thursday Trump administration officials who testified as part of the House impeachment inquiry.

"All of them acted in the best interest of the country as they saw it and consistent to what they thought our policies were," Bolton said during a private event in Austin, Texas, according to CNN affiliate KXAN

His comments came a day before the Senate votes Friday on whether to seek additional witnesses, including whether to hear from Bolton about his explosive allegation in the Ukraine scandal. It became clearer on Thursday night that the Senate trial is all but certain to come to a swift end without hearing from witnesses or subpoenaing documents.

Bolton said members of the Trump administration should "feel they're able to speak their minds without retribution."

"The idea that somehow testifying to what you think is true is destructive to the system of government we have, I think, is very nearly the reverse -- the exact reverse of the truth," he said.

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