Former House Speaker Newt Gingrich told "Fox & Friends" Thursday that the Mueller hearing left him with one obvious question: who actually wrote the report?

"It was very clear he didn't know what was in the report, he clearly didn't have the energy and the focus to have managed a two-year investigation," said Gingrich.

Gingrich, who authored a book called "Collusion," said he found Wednesday's hearings to be "sad" after former special counsel Robert Mueller appeared frazzled and off his game during his highly anticipated testimony, where he discussed the findings of his investigation into Russian interference in the 2016 election.

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Mueller fumbled his way through the rapid-fire questioning, causing many lawmakers to inquire about his team - as it became increasingly clear that he was unfamiliar with details of the report.

After a Republican lawmaker questioned the Democratic leanings of his staff, Mueller fired back.

"I've been in this business for almost 25 years, and in those 25 years, I have not had occasion once to ask somebody about their political affiliation. It is not done," he said.

President Trump claimed on numerous occasions that there were "13 angry Democrats" behind the probe, while Democrats continually claimed Mueller would ensure the fairness of the proceedings.

Gingrich agreed that it was clear Mueller's team had an agenda.

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"It was clear that in very few weeks, he had turned it over to a left-wing anti-Trump group of Democratic lawyers, and my guess is that they were the ones who ran the investigations and made the decisions," he argued.

Gingrich also said he hoped the Attorney General William Barr would investigate who was really making the decisions and who wrote the final report after Mueller appeared to be "weak and confused."