But Priestap told the inspector general that he declined to brief the Trump campaign for fear of compromising the investigation.
Rather, Horowitz found, "FBI officials involved in opening the investigation had reason to believe that Russian Federation may have been connected to the Wikileaks disclosures that occurred earlier in July 2016, and were aware of information regarding Russia's efforts to interfere with the 2016 US elections".
Others investigating the origins of the probe were less charitable.
Democrats said the report showed that the FBI conducted a legitimate investigation.
Those allegations echo, at least in part, the president's frequent claims that his campaign was "spied" on by the Obama administration and that the Russian Federation investigation was a "witch hunt" to kneecap his presidency.
In particular, the report singled out an Federal Bureau of Investigation lawyer who altered an email contained in a renewal of the application which claimed that Page was "not a source" to another US government agency.
"Steele himself was not the originating source of any of the factual information in his reporting".
Even so, it is unlikely that the publication of the review by Inspector General Michael Horowitz will repress the partisan battles that have surrounded Russia's investigation for years. Lawmakers and staff were allowed to begin reviewing the report ahead of its public release.
"We did not find documentary or testimonial evidence that political bias or improper motivation influenced the decisions to open the four individual investigations", the report reads.
Christopher Steele, the British ex-spy and writer of the anti-Trump file, was reportedly instructed that the Justice Division will launch details about him that was beforehand blacked out within the division's inside watchdog report on the investigation into President Trump's 2016 marketing campaign due on Monday.
He said: "The Inspector General's report now makes it clear that the FBI has launched an intrusive investigation into a U.S. presidential campaign on the smallest suspicions that, in my opinion, were insufficient to justify the measures taken". But he said there was "no evidence" that any FBI misconduct "had a material effect on the opening or conduct of this investigation". He has concluded that bias did not taint top FBI leaders running the investigation who have been frequent targets of Trump attacks - including former director James Comey, former deputy director Andrew McCabe and former deputy assistant director Peter Strzok, the people said.
Horowitz said he had no information to support that theory, which has been widely popular in right-wing circles.
Critics of Steele, mainly Republicans, argue that the former MI6 officer who founded the London-based intelligence firm Orbis was biased against Trump and set out to produce a negative report on the then-presidential candidate. Today's report said that was not the case.
Horowitz's office interviewed Steele as part of its investigation.
However, the FBI's surveillance program and how it obtained a FISA (Foreign Intelligence Surveillance Act) warrant were riddled with errors, the report stated, including "17 significant errors or omissions in the Carter Page FISA applications". Durham's work is ongoing.
FBI Director Christopher Wray said he had ordered 40 steps, such as changes to warrant applications and methods for dealing with informants, to fix problems highlighted in the report.
However, on September 19, 2016, the same day that the FBI team received its first memos from former British intelligence officer Christopher Steele, "the team contacted FBI OGC [Office of the General Counsel] again about seeking a FISA order for Page and specifically focused on Steele's reporting in drafting the FISA request".
And in another glaring error, Mr. Steele's main dossier source disagreed with anti-Trump assertions in his dossier after it was posted online in January 2017.
Graham said people should not "judge" the report until Horowitz testifies in front of the Senate Judiciary Committee on Wednesday.
