Buttigieg, who is weighing a 2020 bid, said in an interview with The Washington Post Magazine published in January, "Donald Trump got elected because, in his twisted way, he pointed out the huge troubles in our economy and our democracy." He added, "At least he didn't go around saying that America was already great, like Hillary did."

"America is already great. America is already strong & I promise you, our strength, our greatness, does not depend on Donald Trump." — @POTUS

Nick Merrill, a Clinton adviser and spokesman, called Buttigieg's months-old comments "indefensible."

"This is indefensible. @HillaryClinton ran on a belief in this country & the most progressive platform in modern political history. Trump ran on pessimism, racism, false promises, & vitriol. Interpret that how you want, but there are 66,000,000 people who disagree. Good luck," Merrill posted on Twitter

Buttigieg, 37, has formed a presidential exploratory committee, and if elected would be the youngest president in US history and the first married gay president.

More recently, Buttigieg weighed in on the 2016 election cycle and said in an interview with "The Breakfast Club," a New York City-based radio show, "We spent, I think, way too much time on our side talking about him." He added, "Our whole message was don't vote for him because he is terrible. And even because he is, that is not a message."

Grady Keefe, a former advance staffer for Clinton, criticized Buttigieg as well and wrote on Twitter , "It is unfortunate when people as smart as @PeteButtigieg engage in this fantasy fiction about 2016. And as a gay American it is disappointing because @HillaryClinton ran a campaign which amongst its many values championed our community."

Buttigieg's spokesperson had no comment when reached by CNN.

In a recent interview with CNN's Van Jones on "The Van Jones Show," Buttigieg talked more broadly about being a small town mayor in a red state, and what he believed motivated voters to turn out for Trump in 2016.

He said he believed "there's a sense of hostility to the system, to the economic and political system that we live in -- and that part of what's motivated some of these voters is not wrong.

"Don't get me wrong, I'm not making any excuse for some of the explicit appeals to racism that were made and, in some cases, worked," he continued. "But at the same time, we've also got to recognize that if we come off -- if (Trump's) saying the system is rigged, and the way he's saying it is twisted and not really true, but there's a kernel of truth in there -- and we look like we're the ones saying, oh no, the system is perfectly fine -- then we've got a problem."

He said Democrats are "experiencing this temptation to say, first, you know, this is chaos -- the White House is chaotic, we can't go on like this, it's tearing us apart. That part's true.

"But the second part that is tempting is to say -- therefore, let's go back. Let's go back to normal -- the problem is normal wasn't working for a lot of people," he said.

"Over decades, and Republican and Democratic presidents have let us down and Democrats can't take it back to the '90s, any more than Conservatives can take it back to the '50s."

The interview with Jones is slated to air Saturday at 7 p.m., ET, on CNN.