Washington (CNN) Chief Justice John Roberts on Thursday publicly refused to read a question from Sen. Rand Paul of Kentucky during the Senate impeachment trial that named the alleged Ukraine whistleblower.

"The presiding officer declines to read the question as submitted," Roberts said after receiving the question card.

Paul had expressed frustration with Republican leadership during the trial Wednesday night after it was made clear Roberts would not read his question that named the alleged Ukraine whistleblower , sources with knowledge of the situation said.

The development brought Roberts into an unusual position in the trial, where he has served in large part to guide the proceedings, not to decide or make any rulings on how they progress.

But prior to the 16-hour question-and-answer period for the trial on Wednesday, Roberts made clear that he would not read the alleged name of the whistleblower, nor would he consider questions that would move to clearly identify the individual, the sources said. Roberts, in his role, reads each question submitted by senators.

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