A pair of Fox News contributors sparred Friday over a favorite talking point for the network: immigration and border security, with the duo trading barbs and repeatedly trying to cut each other off, at times appearing to flummox host Martha MacCallum. Appearing on “The Story with Martha MacCallum,” Marc Thiessen and Richard Fowler squared off on immigration and the border. Thiessen is a Washington Post columnist who focuses on foreign and domestic policy and is a fellow at the American Enterprise Institute, and Fowler is a radio host and adjunct journalism professor at Georgetown University. T…