Evan McMullin, the former CIA operative launching a longshot bid for president, said the decision to invade Iraq was "more complicated than people imagine," but ultimately George W. Bush's greatest mistake.

"I served in Iraq and I'm proud of my service there but I believe that that was a mistake," McMullin said Tuesday on "Morning Joe." "I don't think we should have done that. I understand the reasons, I was close to some of those reasons, I understood — I was at the CIA, I heard the justification. I don't think that served our best interest, but I understand. It's more complicated than people imagine, but I understand."

McMullin justified his candidacy by pointing to Hillary Clinton and Donald Trump, both of whom he regards as "unfit" to serve in the White House. But he hesitated to criticized House Speaker Paul Ryan or other Republican leaders who have given their reluctant support to Trump.

"I have the utmost respect for Paul Ryan," McMullin said when asked if Ryan "disappointed" him by endorsing Trump. "I believe he's a true statesman and I'll have to let him explain the way he's handled it but I know that he's in a tough position given his position. ... I believe that I would handled it differently, yes, but I would say that he is in a difficult situation and I understand how and why he's handling the way [he] is."