In the final moments before Robert Mueller’s appearance before House committees, President Trump blasted a sudden change in plans that will allow the former special counsel to have one of his top aides accompany him.

On Tuesday, House Democrats permitted Mueller’s former chief of staff and Deputy Special Counsel Aaron Zebley sit at the witness table. Fox News is told the Intelligence Committee will swear in Zebley before its hearing.

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“It was NEVER agreed that Robert Mueller could use one of his many Democrat Never Trumper lawyers to sit next to him with his answers,” Trump tweeted Wednesday morning. “This was specifically NOT agreed to, and I would NEVER have agreed to it. The Greatest Witch Hunt in U.S. history, by far!”

Earlier in the morning, Trump questioned how Democrats could “illegally fabricate a crime, try pinning in on a very innocent President,” and then accuse him of obstruction “when he fights back against this illegal and treasonous attack on our Country.” And he questioned why Mueller didn't investigate figures inside law enforcement involved in the launch of the original Russia probe.

Republicans have spoken out against the last-minute change of adding Zebley, calling it an “apparent stunt” by Democrats. Rep. Doug Collins, R-Ga., the Judiciary panel’s top Republican, said the move “shows the lengths Democrats will go to protect a one-sided narrative from a thorough examination by committee Republicans.”

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Collins also penned a Tuesday opinion piece for The New York Times, where he slammed Democrats for not accepting Mueller’s report and conducting “empty investigations.” He called the hearings “a Hail Mary that doesn’t have a prayer.”

House Judiciary Committee Chairman Jerrold Nadler, D-N.Y., defended the necessity of having Mueller testify regarding his investigation's findings, telling "Fox News Sunday" that Mueller's report contained "very substantial evidence that the president is guilty of high crimes and misdemeanors."

Fox News' Bradford Betz contributed to this report.