Concord, New Hampshire - Governor Chris Sununu shared some pretty harsh criticisms about presidential candidate Donald Trump as his state prepares to vote in the primaries.

Sununu, who recently endorsed Trump's last standing challenger Nikki Haley, did an interview with CNN on Monday where he argued that the race is "all about the enthusiasm" – something he thinks the former president lacks.

"It's really about the energy of the campaign," he said.

"Trump has no energy. The guy can barely read a teleprompter right now.

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"All the wind is behind Nikki's sails," he added. "So I just think the sky's the limit."

He went on to insist that Haley poses a big threat to Trump as she has been "surging" in polls around the country.

While Sununu told CNN earlier this month that he would vote for Trump if he becomes the Republican nominee – even if he is convicted of a felony before then – he has always been highly critical of the former president.

Trump, on the other hand, took Sununu's endorsement of Haley personally and has been criticizing the governor publicly ahead of the New Hampshire caucuses.

During a recent rally in Portsmouth, Trump described Sununu as "overrated" and claimed to have beaten him "by 44 points" in the primaries, though the governor never formally joined the race because he "didn't have the courage."

"This guy, just so you understand, I was never a fan of his," Trump added.