White House press secretary Stephanie Grisham blasted Robert Mueller's Capitol Hill testimony Wednesday, calling the proceedings an "epic embarrassment" for Democrats.

"The last three hours have been an epic embarrassment for the Democrats. Expect more of the same in the second half," she wrote.

Democrats questioned Mueller about the contents of his report, hoping to steer him to a damning conclusion for President Trump -- while Republicans grilled the former FBI director over what he knew, when he knew it, and if his personal politics ever got in the way of the Russia investigation.

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Mueller mostly remained defiant and reserved, claiming he was unable to answer some of the lawmakers' questions directly for varying reasons.

He was challenged by Rep. Jim Jordan, R-Ohio and Rep. Louie Gohmert, R-Texas, about his personal political bias in the case, and was seemingly so flustered at times he had to continually ask his questioners to repeat themselves.

He was unfamiliar, at one point, with Fusion GPS, the opposition research firm behind the controversial Steele dossier which was used to obtain a FISA warrant against the Trump campaign's Carter Page.

President Trump weighed in via Twitter to satirically thank House Democrats for holding the hearing, and also referred to the spectacle as an "embarrassment."

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"I would like to thank the Democrats for holding this morning’s hearing. Now, after 3 hours, Robert Mueller has to subject himself to #ShiftySchiff - an Embarrassment to our Country!" he wrote.

Fox News' Ronn Blitzer contributed to this report