South Plainfield, N.J. — Governor Chris Christie of New Jersey is open to being tapped as Mitt Romney’s running mate. At a town-hall meeting this afternoon, he played down his chances of being selected but expressed a willingness to “listen,” should Romney ask him to be on the ticket. “There is only one person in my party who gets to make that decision and that’s Governor Romney,” he said. “If Governor Romney comes to me and wants to talk about it, I’ll always listen.”