Sen. Rand PaulRand PaulSenate takes up NATO membership for Montenegro Overnight Defense: Civilian casualties raise questions about rules of engagement | Air Force nominee set for hearing | Senate takes up NATO membership for Montenegro Feehery: Freedom Caucus follies MORE (R-Ky.) on Thursday warned that terrorists from the Islamic State in Iraq and Syria could infiltrate the United States through the southern border.
"We must also secure our own borders and immigration policy from ISIS infiltration," Paul said in an op-ed in Time magazine that outlined his strategy for dealing with the group.
"Our border is porous, and the administration, rather than acting to protect it, instead ponders unconstitutional executive action, legalizing millions of illegal immigrants," he added.
"This is inexcusable over a decade after we were attacked on 9/11 by hijackers including one Saudi student who overstayed his student visa," he said.
Paul called for revoking the visas of any U.S. citizens fighting with ISIS overseas.
His comments echo a warning from another potential GOP presidential contender, Texas Gov. Rick Perry. Perry went further last month, saying that ISIS militants might have already crossed the border, though he acknowledged there is no evidence of that.
The Pentagon has said ISIS has aspirations to hit Western targets, but the military has "seen no indication that they are coming across the border with Mexico. We have no information that leads us to believe that," Rear Adm. John Kirby said last month.
In the op-ed, Paul reiterated that he does not consider himself an interventionist or isolationist. He said he supports expanding airstrikes against ISIS in Syria with approval from Congress.
"The long-term challenge is debilitating and ultimately eradicating a strong and growing ISIS, whose growth poses a significant terrorist threat to U.S. allies and enemies in the region, Europe, and our homeland," he said.
Paul also called for arming Kurdish fighters in Iraq, which the administration is doing, and building a coalition of nations to help with the threat.
"This is one set of principles. Any strategy, though, should be presented to the American people through Congress," he said. "If war is necessary, we should act as a nation."