Senate Judiciary Chairman Charles E. Grassley released documents Monday concluding that the FBI under Director James B. Comey failed to investigate fully Hillary Clinton’s use of a private email server and mishandling of highly classified information.

The finding was first made by the Justice Department Office of Inspector General.

The newly declassified “Clinton annex” is an appendix to the inspector general’s June 2018 report reviewing the DOJ and FBI’s handling of the Clinton email investigation.

The current Justice Department, under the leadership of Attorney General Pam Bondi, and other agencies declassified and provided the Clinton annex to Mr. Grassley, Iowa Republican, at his request.

The inspector general’s Clinton annex shows the FBI obtained thumb drives from a source during the Clinton investigation.

But Mr. Comey, as well as then-Deputy FBI Director Andrew McCabe, former FBI Special Agent Peter Strzok and others, did not perform additional, targeted searches of the drives, even though the drives contained information pertinent to the inquiry.

“This document shows an extreme lack of effort and due diligence in the FBI’s investigation of former Secretary Clinton’s email usage and mishandling of highly classified information,” Mr. Grassley said.

He continued, “Under Comey’s leadership, the FBI failed to perform fundamental investigative work and left key pieces of evidence on the cutting room floor.”

“The Comey FBI’s negligent approach and perhaps intentional lack of effort in the Clinton investigation is a stark contrast to its full-throated investigation of the Trump-Russia collusion hoax, which was based on the uncorroborated and now discredited Steele dossier. Comey’s decision-making process smacks of political infection.”

Mr. Grassley had been requesting the information about the document from Justice and the FBI since 2018 and subsequently submitted his request to then-Attorney General Bill Barr in 2019.

He and Sen. Ron Johnson, Wisconsin Republican, requested President Trump declassify the document in 2020, and Mr. Grassley, again, requested the document in 2025.

The inspector general’s report shows that the FBI failed to thoroughly and completely investigate the Clinton matter, as well as comb through the serious national security risks created by Mrs. Clinton’s handling of highly classified information.

According to the inspector general, the thumb drives contained highly sensitive information extracted from U.S. government agencies, including the Department of State, as well as then-President Barack Obama’s emails and, potentially, congressional information.

The thumb drives were never evaluated as part of the Clinton email probe, despite the recommendation of a draft FBI memorandum.

The report also said the drives should have been immediately reviewed for foreign intelligence purposes, but were never evaluated.

On July 5, 2016, Mr. Comey absolved Mrs. Clinton in a public statement about the investigation and recommended the Justice Department take no legal action against her.

However, according to Mr. Grassley, Mr. Comey had planned to exonerate Mrs. Clinton before FBI officials had even interviewed her.

Several weeks later, on July 31, 2016, Mr. Comey’s FBI formally opened the Crossfire Hurricane investigation into President Trump’s later disproven collusion with Russia.

On that day, Mr. Strzok texted Lisa Page, an FBI lawyer, saying: “And damn this feels momentous. Because this matters. The other one did, too, but that was to ensure we didn’t F something up. This matters because this MATTERS. So super glad to be on this voyage with you.”

However, according to previous news reporting, rank and file FBI agents grew agitated with how Mr. Comey orchestrated the investigation into the Clinton email server. By October 2016, one month before the election, agents were becoming alarmed over Mr. Comey’s recommendation.

“This is a textbook case where a grand jury should have convened but was not. That is appalling,” an FBI special agent who has worked public corruption and criminal cases said of the decision. “We talk about it in the office and don’t know how Comey can keep going.”

The agent was also shocked that the bureau did not bother to search Mrs. Clinton’s house during the investigation.

“We didn’t search their house. We always search the house. The search should not just have been for private electronics, which contained classified material, but even for printouts of such material,” he said.

“There should have been a complete search of their residence,” the agent pointed out. “That the FBI did not seize devices is unbelievable. The FBI even seizes devices that have been set on fire.”

The Washington Times has reached out to Mr. Comey for comment. The FBI declined to comment to The Times.

• Kerry Picket can be reached at kpicket@washingtontimes.com.