The FBI made significant errors in 2016 when it sought to monitor a former Trump campaign adviser, an internal watchdog said, as part of what it found to be a justified probe into links between the Trump campaign and Russia.

The report’s scathing assessment of the FBI’s actions make it likely to further inflame a partisan debate about the propriety of the agency’s investigation into Trump campaign associates. The Justice Department’s inspector general found the FBI had information that undercut material it was relying on from a controversial former British intelligence officer, Christopher Steele, but withheld it from both the Justice Department and a secret U.S. court in charge of approving the surveillance.

In the report of more than 400 pages released on Monday, the inspector general said the Federal Bureau of Investigation had reason to open its initial investigation in July 2016 into links between the Trump campaign and Russia’s interference in the presidential election. The IG’s report also included no evidence that political bias influenced decisions made in the FBI’s inquiry.