WASHINGTON — The Justice Department’s internal watchdog was caught in a political tug of war Wednesday as Republican and Democratic senators used his report on the origins of the Russia investigation involving Donald Trump’s 2016 campaign to support their views that it was a legitimate probe or a badly bungled farce.

Inspector General Michael Horowitz testified before the Senate Judiciary Committee about his findings that while the FBI had a legitimate basis to launch the investigation and was not motivated by political bias in doing so, there were major flaws in how that investigation was conducted.

The hearing was the latest reflection of Washington’s intense politicization. Senators from both parties praised a detailed, nuanced report by a widely respected, nonpartisan investigator, while pressing him to call attention to findings that back their positions.

Horowitz himself tried to strike a balance. He insisted that the FBI should not feel comforted by his findings and pointed out the absence of evidence for some of the most sensational claims by Trump and his supporters: that the investigation into ties between his presidential campaign and Russia had been opened for political reasons, that agents had infiltrated his election bid or that former President Barack Obama had directed a wiretap of the Republican candidate.

Still, his opening statement was overwhelmingly critical of the investigation, and he returned time and again throughout the hearing to serious problems that he said underscored the need for policy changes at the FBI.

Among them, he said, were flaws and omissions in how the FBI prepared its applications for court approval to eavesdrop on a former Trump campaign aide, as he rebuked officials for failing to update judges as they learned new information that undercut some of their original assertions.

“It doesn’t vindicate anybody at the FBI who touched (the applications), including leadership,” Horowitz said. That was a rejection of the views of former FBI Director James Comey, who had claimed vindication for the bureau based on Horowitz’s conclusions.

Republicans and Democrats pressed Horowitz on whether he believed the FBI had acted with partisan bias. His response was hedged: He said the multitude of errors during the surveillance warrant process, which included the altering of an email by an FBI lawyer, was so “inexplicable” and yielded no obvious explanations that he could not be confident about the intention.

Even so, Horowitz also repeatedly noted under questioning from Democrats that he had not found that the FBI had targeted Trump for investigation for political reasons. The investigation was opened for a proper cause, he said, after the FBI received information that a Trump campaign aide had been told that Russia had information that could hurt the presidential campaign of Trump’s Democratic rival, Hillary Clinton.