According to President Trump's former chief of staff, he thinks an impeachment trial with no witnesses should only be considered "half a trial," NJ.com reports.

"In my view, they kind of leave themselves open to a lot of criticism," John Kelly said in an interview. "It seems it was half a trial."

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Kelly says he believes new revelations from Bolton's upcoming book that Trump played a central role in a campaign to pressure Ukraine to announce an investigation into the Bidens.

"If I was advising the United States Senate, I would say, 'If you don't respond to 75 percent of the American voters and have witnesses, it's a job only half done," he added. "You open yourself up forever as a Senate that shirks its responsibilities."