Sen. Rand Paul (R-Kentucky). CNN/screenshot US Sen. Rand Paul (R-Kentucky) went after front-runner Donald Trump with his opening statement at the Republican presidential debate on Tuesday night.

Paul attacked Trump, who is leading in polls for the Republican presidential nomination, over his suggestion that we should "close up" parts of the internet to counter ISIS recruitment.

The terrorist group ISIS — aka the Islamic State, ISIL, and Daesh — uses social media and other internet platforms to recruit Westerners to carry out attacks and travel to the territory the group holds in the Middle East.

"The question is: How do we keep America safe from terrorism? Trump says we ought to close that internet thing," Paul said. "The question really is: What does he mean by that? Like they do in North Korea? Like they do in China?"

Paul also went after another leading Republican, Sen. Marco Rubio (R-Florida).

"Rubio says we should collect all Americans' records, all of the time," Paul said. "The Constitution says otherwise. I think they're both wrong. I think we defeat terrorism by showing them that we do not fear them."

Circling back to Trump's suggestion, Paul hinted that his proposed policy would be counterproductive.

"I think if we ban certain religions, if we censor the internet, I think that at that point, the terrorists will have won," Paul said.