Rubio Strikes Back at Trump

While other GOP candidates this summer were busy calling Donald Trump a "fake conservative" or saying they'd "beat his brains out," Marco Rubio was keeping his head down, at times even avoiding to utter Trump's name.

Not anymore.

After months of playing coy, Rubio is fighting back.

"I'm not interested in the back and forth, to be a member or a part of his freak show. He is a very sensitive person, he doesn't like to be criticized," Rubio said on Monday on NPR.

"He had a speech in South Carolina to an empty crowd, he got booed on Friday at that Values Voters Summit, his poll numbers have taken a beating and he was embarrassed on national television at the debate by Carly Fiorina and others," Rubio went on.

Over the weekend, Rubio also called Trump "thin-skinned," "sensitive," and said Trump was "reacting really poorly to adversity."

And while other candidates found it difficult to take on the Donald this summer without doing themselves some damage (Graham, Perry, Bush), the Trump- Rubio faceoff seems to be doing Rubio some good.

At the Values Voters Summit over the weekend, Trump was booed loudly when he referred to Rubio as a "clown" (that same crowd had given Rubio a standing ovation just two hours earlier).

Trump has also attacked Rubio for being too young and too ambitious, calling him a "lightweight," and a "baby"; yet his attacks have done nothing to hurt Rubio's poll numbers, which have almost doubled since the second GOP debate (from 6 percent to 11 percent).

The Trump-Rubio feud began when Rubio was asked on Fox News whether Trump knew enough about national security to be president.

"I think up to now he hasn't really answered serious questions about national security," said Rubio. "And until he does there should be concerns."

Rubio however has not gone after Trump in any of his speeches, and has only responded to Trump when specifically asked about him by the press.

"Obviously from time to time we'll respond to something that needs to be answered but by and large, I'm focused on America, this is about America not about the individuals running," Rubio told reporters on Monday after an event in The Villages, Florida.

"We spend 99.9 percent of our time in this campaign talking about the issues that matter to America. This campaign is about our people and our country- not about any individual personalities," he said.