Ahead of Justice Department Inspector General Michael Horowitz's testimony before the Senate Judiciary Committee on Wednesday, Sen. Ted Cruz, R-Texas, said that this marks a sad day for the department and that he disagrees with the watchdog report's conclusions about political bias not playing a role in the FBI's Russia investigation.

"It is over 500 pages long and it details over and over and over again, the blatant misconduct, unfortunately, at the FBI and the Department of Justice," Cruz said. "It details 17 serious misstatements that the FBI Department of Justice made to the FISA court, statements that just weren't backed up by facts."

Appearing on "America's Newsroom" with host Bill Hemmer, Cruz said that while he believes Wednesday's hearing is "going to be very valuable," the Foreign Intelligence Surveillance Act (FISA) report released by Horowitz on Monday was "nothing short of stunning."

IG MICHAEL HOROWITZ TESTIFIES BEFORE SENATE JUDICIARY COMMITTEE: LIVE UPDATES

The review about the origins of the Russia investigation determined that the FBI complied with policies in launching the politically explosive probe but also flagged "significant concerns with how certain aspects of the investigation were conducted and supervised."

In his opening statement, Horowitz wrote Wednesday that he was "deeply concerned that so many basic and fundamental errors were made by three separate, hand-picked investigative teams; on one of the most sensitive FBI investigations; after the matter had been briefed to the highest levels within the FBI; even though the information sought through use of FISA authority related so closely to an ongoing presidential campaign; and even though those involved with the investigation knew that their actions were likely to be subjected to close scrutiny."

Cruz told Hemmer that the "best you can conclude" after a pattern of "misstatement after misstatement after misstatement" is that the agencies were "grossly negligent and incompetent and took, with the most cavalier lack of concern, launching an investigation into a political opponent."

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In addition, Cruz disagreed with Horowitz's final conclusion that political motivation didn't play a role in decision-making.

"I think it's clear the senior leadership there were hard Democratic partisans because it's the only way you justify sending in spies, confidential informants to spy on the Trump campaign," he said. "This is when he is the Republican nominee for president, he is the leading contender on the Republican side. And the FBI is sending in spies to spy on his campaign."

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"They're authorizing in October of the election year, a wiretap; that was abusive -- particularly when they knew the basis of it," Cruz continued. "They had the underlying fact as the basis of it was unreliable and was being paid for by the Hillary Clinton campaign that they were being a conduit for oppo research from the other campaign.

"It's a sad day for DOJ right now."

Fox News' Adam Shaw, Ronn Blitzer, Alex Pappas, and Brooke Singman contributed to this report.