Kentucky Senator Rand Paul is the favorite of the small-government movement, and Republican rivals are starting to gang up on him to argue that he could dim the party's chances against a Democratic Party unified behind Hillary Clinton.

"It feels good to be the anti-establishment figure until the entire establishment comes raining down on you, and that's what they're going to do to him," radio talk show host Laura Ingraham said of Paul in an interview. "I'm a little surprised it's happening so early."

Texas Governor Rick Perry delivered a rebuke of Paul in the Washington Post, casting him as an isolationist who would let terrorism fester beyond U.S. borders.

Paul is "curiously blind" to the threat of the Islamic State in Iraq and "drawing his own red line along the water's edge, creating a giant moat where superpowers can retire from the world," Perry wrote in a July 11 opinion piece.