Former Maryland Gov. Martin O'Malley believes there are "legitimate questions" that still need to be answered about fellow 2016 Democratic presidential contender Hillary Clinton's use of a private email system during her tenure as secretary of state, a scandal O'Malley said has been detrimental to the Democratic party.

"I believe that there are a lot of legitimate questions still to be answered about this particular controversy, the email, the email server, the FBI investigation and the like," O'Malley told CNN's Jake Tapper, reported The Hill.

Last week, the Obama administration discovered that Clinton failed to turn over all work-related emails sent from her personal account as she claimed and then reaffirmed upon signing a sworn statement under penalty of perjury, reported The Associated Press.

Clinton said on Sunday that she could not explain that missing chain of work-related emails, which was exchanged in January and Febuary 2009 with retired Gen. David Petraeus.

"There was a transition period. You know, I wasn't that focused on my email," Clinton said on NBC's "Meet the Press," reported The New York Times.

O'Malley said the controversy threatens to distract from more important issues, which is why he says the Democratic National Committee needs to sanction more than six presidential debates.

"It's so important that as Democrats we start having debates about other issues as well," O'Malley said. "I'm not saying there aren't legitimate questions to be answered here by Secretary Clinton, but for our part as a party, we need to talk about the things that will actually get wages to go up rather than down, that people care about around their kitchen tables...that's why we need to have debates."

"Otherwise, our party is being defined by Hillary Clinton's email scandal, and it's not good for our country," he said.

O'Malley also criticized Clinton for waiting so long to announce her opposition to the Keystone XL pipeline, saying she shouldn't "wait for focus groups" before making her positions known.

"I came out against the Keystone pipeline over a year ago. Why? Because I believe it's contrary to our nation's best interests of moving forward to a clean energy future," O'Malley said, according to CNN.

"That's what real leadership is about," he added. "That's the sort of new leadership we're looking for. Not the sort of leadership that waits for poll numbers or focus groups or puts a finger in the air to see which way public opinion is going. No, that's not leadership."