Sen. Rand Paul (R-KY) used his hard-earned spot on the GOP debate main stage to lay into Sen. Marco Rubio (R-FL) on immigration, earning cheers from the crowd.

Paul pivoted from a question on why he didn’t support increasing surveillance to accuse Rubio of weakening U.S. security, pointing specifically to his failed immigration legislation known as the “Gang of Eight” bill.

“Marco has opposed at every point increased border security for those who come to our country. On his Gang Of Eight bill, he would’ve liberalized immigration,” Paul said. “And he steadfastly opposed any new border security requirements from refugees or students. Last week, I introduced another bill saying we need more security, we need more scrutiny. Once again Marco opposed this.”

Paul accused Rubio of trying to “have it both ways.”

“He thinks he wants to be this ‘Oh I’m great and strong on national defense’ but he’s the weakest of all the candidates on immigration. He’s the one for an open border that is leaving us defenseless,” Paul said. “If we want to defend the country, we have to defend against those who are coming in. Marco has more of an allegiance to Chuck Schumer and to the liberals than he does to conservative policy.”

Paul had previewed the line of attack in an interview for Breitbart earlier Tuesday.