"Calm down, Senator," McCain said, in an apostrophe to Paul. "The U.S. government cannot randomly target U.S. citizens."

In his filibuster Wednesday, Paul criticized the White House over its drone policies, and for refusing to rule out military strikes against U.S. citizens on American soil.

McCain, a staunch foreign policy hawk, said Thursday that Paul's warnings that the U.S. could target "Jane Fonda" or "people in cafes" bring the debate into the "realm of the ridiculous."

"If Mr. Paul wants to be taken seriously he needs to do more than pull political stunts that fire up impressionable libertarian kids," McCain said, adding: "I don't think what happened yesterday is helpful to the American people."