WASHINGTON – Former FBI Director James Comey spoke out in an interview with NBC News Wednesday where he defended the rationale for special counsel Robert Mueller investigating possible collusion between the Trump campaign and Russia.

Comey, who oversaw the investigation before Mueller and whose firing by President Donald Trump became a component of the investigation, told NBC's Lester Holt that "There was smoke and enough smoke to justify investigating."

"The investigation had to happen. It would have been irresponsible not to investigate. And we don’t investigate, despite what the partisans say, to find a particular result," Comey said. "We investigate to find out what’s true, and as best I can tell, it looks like Bob Mueller was allowed to do that, and that’s a great thing."

He said there is a certain level of partisan hypocrisy in denouncing the investigation and claiming it should not have happened, even suggesting that Republicans would demand an investigation if it were Barack Obama accused of having ties to a foreign power while running for president.

"Obviously, there was overwhelming evidence the Russians were interfering in the election to hurt one candidate and to help the other," Comey said. "Whether Americans were conspiring with him, I didn’t know, but we had to look at that.”

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Comey said Mueller's careful results, which were outlined in a letter by Attorney General William Barr on Sunday, reaffirmed that the FBI was not out to get Trump and were only after the truth.

He said the investigation "establishes, I hope, to all people no matter where they are on the spectrum, that the FBI is not corrupt, not a nest of vipers, of spies, but an honest group of people trying to find out what is true."

As part of its Russia investigation, the FBI opened an obstruction of justice probe into Trump shortly after he fired Comey in 2017. The investigation centered on Comey's firing along with remarks and directions Trump had given over the years, including telling Comey, "I hope you can let it go," referring to an investigation into Trump's former National Security Advisor Michael Flynn.

In a March interview with USA TODAY, Comey said while he saw evidence of obstruction of justice in Trump's treatment of him, he said he didn't know if it reached the threshold of a criminal violation.

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Comey said he was confused why Mueller and his office could not determine whether Trump obstructed justice, instead just listing out both sides of the argument for criminal charges.

Barr, in a letter to Congress, said he and Deputy Attorney General Rod Rosenstein examined the evidence, discussed it internally within the Justice Department and concluded that evidence was "not sufficient to establish that the President committed an obstruction-of-justice offense."

"The part that's confusing is, I can't quite understand what's going on with the obstruction stuff," Comey said Tuesday evening at an event in Charlotte, N.C., according to NBC News. "I have great faith in Bob Mueller, but I just can't tell from the letter why didn't he decide these questions when the entire rationale for a special counsel is to make sure the politicals aren't making the key charging decisions."