CNN historian lays waste to GOP defense of Trump stonewalling: 'Largest cover-up of impeachment in history'

A presidential historian identified two key differences between President Donald Trump's impeachment trials and the two others in history -- and dismissed Republican arguments against hearing evidence as "nonsense."

Canadian-American historian Tim Naftali told CNN that Trump's impeachment trial differed greatly from its two predecessors, and knocked down GOP defenses of the president.

"There are two big, big considerations out there that the public should have in mind when they list to the debate, if they do later today," Naftali said. "One, this is the first time the president's party has ever controlled a Senate trial in the history of the United States -- it's never happened before. Either it was the other party, or it was a faction, in the case of Andrew Johnson."

The Republicans are understandably nervous about additional evidence, Naftali said, so they're trying to set up protections from the start.

"The second big difference is, that we witnessed the largest cover-up, the largest stonewall of an impeachment in history during the House period of this," Naftali said.

"The president didn't respond to one subpoena," he added. "That's unprecedented. Richard Nixon didn't get to the trial stage, but he did respond to subpoenas for documents."

CNN anchor Anderson Cooper pointed out that former GOP senator Rick Santorum argued that Barack Obama had fought subpoenas as president, but Naftali said that comparison fell apart.

"There is something different about impeachment," Naftali said. "Yes, there will be a struggle between the executive branch and the legislative branch ... There has always been a push and pull between the two branches, of course, but this is different, this is special -- and our founders understood it as much. I don't think the Obama argument is useful at all."

Trump's stonewalling made additional testimony and evidence essential in the impeachment trial, the historian argued.

"If you have this massive stonewall, the Senate has the power in our Constitution, to be an active player in judging a president," Naftali said. "The idea that it's supposed to be passive, supposed to, in the words of Adam Schiff, read the cold record of a grand jury and live with it, is nonsense. All those senators know that the White House has stonewalled. They have an obligation to the public to try to get the information."