An ex-wife of Newt Gingrich told ABC News’s “Nightline” that the Republican presidential candidate wanted an “open marriage.” In a published clip of Brian Ross’s interview with Marianne Gingrich, which will air tonight, Marianne Gingrich said her husband wanted her to accept the fact that he had a mistress. “He was asking to have an open marriage and I refused,” she said. Marianne Gingrich said Newt Gingrich admitted to his six-year affair with Callista, a congressional aide who is now married to the candidate. Newt Gingrich allegedly said Callista “doesn’t care what I do.” Asked for her response, Marianne Gingrich...