WASHINGTON – Birtherism’s back. But it’s tired. At least at the U.S. Capitol. Ahead of Monday’s Iowa Republican caucus, former President Donald Trump has pulled out his old xenophobic playbook and is questioning the citizenship of former Gov. Nikki Haley (R-SC) – Trump’s own former ambassador to the United Nations. On Monday, Trump reposted a piece from the fringe-right, conspiracy-peddling Gateway Pundit falsely questioning Haley’s citizenship status. But even Trump supporters on Capitol Hill are dismissing the lie. “Nope,” Sen. Lindsey Graham (R-SC) – Trump’s 2016 primary opponent who endors…