Photo via CBS News Although there were several procedural errors, the FBI was justified and lacked political bias when it launched its investigation into Russian interference in the 2016 election and the Trump campaign’s ties to Russia, the Department of Justice inspector general (IG) found in a report published Monday. Michael Horowitz, the Justice Department’s IG, will testify about his conclusions on Capitol Hill on Wednesday. The Republican-controlled Senate Judiciary Committee is expected to question him about the FBI’s procedural errors discovered and analyzed by his team. President Trump has accused the FBI of harboring a bias against him. Horowitz’s report was released as Mr. Trump faces the possibility of impeachment by House Democrats. On Tuesday, the House unveiled two articles of impeachment related to the president’s dealings with Ukraine. The 434-page Horowitz report is based on more than 1 million documents from the Justice Department and the FBI as well as interviews with more than 100 witnesses. Attorney General William Barr immediately challenged its findings. “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,” he said in a statement. FBI Director Christopher Wray, however, accepted the report’s findings and acknowledged that “certain FBI personnel” had failed to comply with the FBI’s policies and standards of conduct. He said he has “ordered more than 40 corrective steps to address the report’s recommendations.” The Horowitz report isn’t the final word on the investigation. U.S. Attorney John Durham is leading a separate review of it, and Durham, too, questioned Horowitz’s conclusions. “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,” Durham said in a statement. Durham noted that his investigation includes information from other entities outside the Justice Department, “both in the U.S. and outside of the U.S.” Unlike the Horowitz or Mueller reports, Durham’s probe is a criminal investigation, which gives him the authority to issue subpoenas for witnesses and documents, and to call a grand jury. Lindsey Graham: “Everyone involved in this investigation hated Donald Trump” 8:30 a.m.: Senate Judiciary Committee Chairman Lindsey Graham told CBS News’ Catherine Herridge that he believes the FBI’s Russia investigation crossed the line and sets a bad precedent. “Here’s what I don’t understand about Horowitz: I think he’s a patriot, I think he did a hell of a job here, but when he says that there’s no evidence of political bias or political motive — everybody involved in this investigation hated Donald Trump,” Graham said. He added, “They wanted to bring down this president. I really believe that.” Asked whether he planned to press Horowitz on this point, Graham replied, “One it doesn’t matter why they did it. I want people to understand that the cops can’t cheat. The cops can’t lie. They have to play by the rules. Even if you don’t like Trump you should like the rules because it could be you next time, not Trump.” How to watch Michael Horowitz’s Senate testimony Date: Wednesday, December 11, 2019 Time: 10 a.m. ET Who: Michael Horowitz, inspector general for the Justice Department Online stream: CBSN — live in the player above and on your mobile or streaming device On TV: WINK News