Sen. John McCainJohn Sidney McCainAfghanistan is our longest war ever and Congress has abandoned all responsibility Kremlin: ‘We have a long way to go’ before any breakthrough with US The GOP is Trump's party now MORE (R-Ariz.) suggested Sunday that Sen. Rand PaulRandal (Rand) Howard PaulSenate approves .3 trillion spending bill, sending to Trump GOP senator threatened to hold up bill over provision to honor late political rival: report Conservatives balk over funding bill ahead of shutdown  MORE (R-Ky.) had little credibility in the fight against terror, saying that the Boston bombing had proved his views wrong.

McCain, in an interview on CNN's State of the Union, was asked to respond to Paul’s statements calling the National Security Agency’s phone tracking program an "all-out assault on the Constitution."

"Right. Just prior to the Boston bombing, he said the battlefield was no longer in America," McCain said. 

McCain's comment referenced an interview with Fox News where Paul criticized members of his party for saying that the fight against terror must be global in nature. 

"President Obama says this," Paul said in that interview. "Some members of my party say the battle has no geographic limitations and the laws of war apply. It's important to know that the law of war that they're talking about means no due process."

McCain also criticized Paul over Iran policy, saying “he's the only one that voted that Iran must not be just contained in pursuit of nuclear weapons. I disagree."

Paul has been a sharp critic of the NSA’s surveillance of phone calls and the internet. But McCain defended those programs Sunday as critical to U.S. security.

McCain and Paul have repeatedly clashed over national security. 

After Paul held a 13-hour filibuster on John Brennan's nomination to run the CIA over the nation’s drone policy, McCain called Paul and Sen. Ted CruzRafael (Ted) Edward CruzConservatives balk over funding bill ahead of shutdown  Confirmation fight over Trump pick exposes blurred lines in GOP-LGBT activism GOP pushes to change Senate rules for Trump MORE (R-Texas), who joined the filibuster, "wacko birds."

Paul last week mocked McCain’s secret trip to Syria to meet with opposition forces after photos appeared showing McCain with two men accused of kidnapping Shiite civilians.

“We had a senator over there who had his picture taken with some kidnappers, so I don’t know how good a job we’re doing vetting those who are going to get the arms,” Paul said in a speech criticizing McCain’s call to arm pro-Western Syrian rebel groups.