(CNN) Filmmaker Michael Moore said Thursday that Democrats should not focus solely on the FBI's handling of the investigation into Hillary Clinton's private email server as the reason why they lost the White House.

"Democrats are doing themselves a disservice if they just focus on the Comey thing and not on all the other reasons this happened," Moore told CNN's Don Lemon on "CNN Tonight with Don Lemon."

Thursday, the Justice Department inspector general said he was looking into the FBI's decision to reopen the investigation into Clinton's private email server, just days before the election.

Democrats say that move contributed to Clinton's loss. But Moore, a Clinton supporter, suggested the investigation was just part of the picture.

"Obviously, this had an impact in the final week of the election," Moore said. "It's not the only thing though. It's disgraceful that twice in 16 years the Democrats have won the popular vote and somehow lost the electoral college. That they would let this happened again. That nobody did the math, nobody thought this out, everybody knew what the law was. Hillary didn't go to Wisconsin for seven months."

Read More