Republican presidential candidate Marco Rubio took a jab at GOP front-runner Donald Trump at a campaign stop in New Hampshire, saying the real estate tycoon is not "ready" to become the leader of the free world.

The Florida senator didn't hold back when asked to give his opinion of Trump during a sit down with voters at a diner in Manchester, reports ABC News. That's when Ron Morrison pressed him to give a straight answer about the reality TV star.

"I don't think he's ready to be president of the United States," Rubio said.

"We have a right to be angry and upset about the direction of our country," he said. "But that alone won't be enough. You gotta know what you're going to do about it."

The junior senator also took a stab at Trump's campaign slogan, "Make American Great Again!" describing it as an empty promise that lacks substance.

"We owe it to you to tell you exactly what we're gonna do. And it can't just be, 'Oh we're gonna make everything great again,'" Rubio said.

At one point during the discussion, the conversation shifted toward former Alaska Gov. Sarah Palin, who officially endorsed Trump earlier this week.

"I like Sarah Palin. She doesn't always say nice things about me, but I like her very much," Rubio said when asked for his opinion of her.

"Oh say it -- 'she's an idiot,'" one of the diners chimed in. However, Rubio pushed backed, insisting that he likes the former Republican vice presidential nominee.

"No, I don't believe that, I don't believe that at all," he said, adding he's never met her. "I love her spunk and her energy."

Rubio also took a shot at the billionaire businessman on Friday, saying that he is not a "movement conservative."

"I don't think Donald is running as a movement conservative," Rubio told Fox News anchor Martha MacCallum, according to Politico. "I don't think he's ever said that. It's clear he's not. I mean, what he's running [as is] someone who's a populist, who's upset about the direction of this country - as am I, as are millions of Americans."

He went on to argue that not only does he offer the Republican Party "consistent conservatism, real conservatism," but he also has "the ability to beat Hillary Clinton."