In his long-awaited report into the origins of the 2016 Russia probe, Justice Department Inspector General Michael Horowitz found "serious performance failures" by some FBI officials, but ultimately concluded that the investigation was not tainted by political bias.

Why it matters: President Trump and his allies have long believed that Horowitz would find bias and wrongdoing at the top ranks of the FBI, advancing allegations that the Russia investigation was a politically motivated hit job. While Horowitz does rebuke some low-level officials for carelessness and impropriety while filing surveillance applications, his report ultimately concludes that the basis for the FBI's investigation was legitimate.

Highlights:

Horowitz found that the FBI's opening of cases into Trump campaign officials George Papadopoulos, Carter Page, Paul Manafort and Michael Flynn were not influenced by "political bias or improper motivation."

However, there were "significant inaccuracies and omissions" in the surveillance applications used for Page. Had FBI officials notified Justice Department leadership of certain relevant information, Horowitz said it may have undercut the claims supporting probable cause in Page's application.

Horowitz determined that the controversial Steele dossier did not play any role in the FBI's opening of the investigation, but it did play a "central and essential role" in FBI lawyers' decision to support the Page surveillance request. Horowitz concluded that the FBI fell short in ensuring that Steele's information was accurate.

Steele defended his reports to Horowitz as not designed to be "finished products," and called allegations that he was biased against Trump "ridiculous." Steele claimed that if anything, he was "favorably disposed" toward the Trump family because he had been friendly with one family member for years, which ABC News has reported is Ivanka Trump.

The FBI was interested in obtaining surveillance warrants for Papadopoulos, but ultimately did not. Horowitz found no evidence the FBI sought warrants for Manafort or Flynn.

The report found that the FBI used Confidential Human Sources (CHS) to monitor meetings with members of the Trump campaign. However, those operations "received the necessary approvals under FBI policy" and there were no informants placed within the Trump campaign, Horowitz concluded.

Two of the FBI's targets were already the subjects of federal investigations by the time the Russia probe was opened. Page was the subject of a counterintelligence investigation due to his Russian contacts and Manafort was being investigated for money laundering — two months before he joined the Trump campaign.

What they're saying: While lawyers for former FBI officials Andrew McCabe and Peter Strzok affirmed in statements that the report found no wrongdoing, Attorney General Bill Barr rejected the inspector general's conclusions.

The Inspector General’s report now makes clear that the FBI launched an intrusive investigation of a U.S. presidential campaign on the thinnest of suspicions that, in my view, were insufficient to justify the steps taken. It is also clear that, from its inception, the evidence produced by the investigation was consistently exculpatory.”

— Attorney General Bill Barr

John Durham, the veteran prosecutors assigned by Barr to conduct a more sweeping investigation into the origins of the Russia probe, also cautioned in a statement that he does not agree with all of Horowitz's findings.

"I have the utmost respect for the mission of the Office of Inspector General and the comprehensive work that went into the report prepared by Mr. Horowitz and his staff. However, our investigation is not limited to developing information from within component parts of the Justice Department. Our investigation has included developing information from other persons and entities, both in the U.S. and outside of the U.S. Based on the evidence collected to date, and while our investigation is ongoing, last month we advised the Inspector General that we do not agree with some of the report’s conclusions as to predication and how the FBI case was opened.”

— U.S. Attorney John Durham

Between the lines: The report will not completely satisfy either side of the partisan divide that has endured in the years since the Russia investigation.

Horowitz debunks the conspiracy theory that the so-called "Deep State" was out to get Trump, but he also chastises FBI officials for failing to meet standards for highly intrusive surveillance activity.

Many of the president's allies will point to Durham's pending investigation as a far more comprehensive and damaging probe, but there is no indication as of yet that these claims will bear out.

Read the report.