Sen. Chris Van Hollen (D-Md.) told CBS News' "Face the Nation" Sunday that Republicans are "deathly afraid" of calling impeachment fact witnesses like former national security adviser John Bolton because their sworn testimonies would make it "harder for those senators to vote for acquittal."

"The reason Republicans are so deathly afraid of sending down these fact witnesses is because after they testify — under oath, they'll have to raise their right hand just like all the witnesses in the House did and testify under penalty of perjury — it's going to be much harder for Republicans to hide behind this myth that this was a perfect phone call. And it will make it harder for those senators to vote for acquittal."

— Chris Van Hollen

The big picture: Senate Majority Leader Mitch McConnell (R-Ky.) rejected Minority Leader Chuck Schumer's (D-N.Y.) request for Bolton, acting Chief of Staff Mick Mulvaney and two other White House officials to testify in the impeachment trial.

Those witnesses were blocked by the Trump administration from testifying in the House impeachment inquiry, but they would have direct knowledge of the president's decision to freeze military aid to Ukraine.

McConnell, who has been closely coordinating with the White House, is expected to hold a short trial and call no new witnesses, arguing that it is the House's job to investigate. However, it only requires a majority of senators to vote to call a witness.

The Senate is ultimately expected to acquit Trump, but defections on the decision to call witnesses by moderate Republicans like Sens. Mitt Romney (R-Utah) and Susan Collins (R-Maine) could shake up the trial.

Van Hollen told CBS he will "wait to hear all the evidence" before deciding how to vote on removing Trump from office, but said he believes the House has made a "very strong case for impeachment."

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