Washington (CNN) Democratic Sen. Sherrod Brown on Sunday said it would be "fine" if Senate Republicans requested Hunter Biden as a witness in the impeachment trial against President Donald Trump in exchange for House Democrats' requested witnesses.

Brown, though, added in his comments on "State of the Union" that he's not sure what value testimony from the son of former Vice President Joe Biden would provide.

"I think you bring in -- We take the position that we want to hear from the witnesses. I don't know what Hunter Biden has to do with the phone call the President made.." the Ohio Democrat told CNN's Brianna Keilar, adding: "The point is we need witnesses, we need to know who they are with the right to call witnesses, additional witnesses later. But I don't understand how you come to the American public, make the case that this is a real trial, if there are no witnesses and there is no new evidence."

The impeachment trial is set to begin in earnest Tuesday and the Senate is expected to pass a resolution outlining the rules of the impeachment trial with only with Republican votes. Though the text of the resolution hasn't been released, it's expected to punt the question of calling witnesses until after opening arguments and senators' questions, while including an opportunity to vote on whether the Senate should have witnesses.

Trump and congressional Republicans have criticized House Democrats for not allowing Hunter Biden to be called as a witness during the impeachment hearings.

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