New York Rep. Elise Stefanik has accepted President-elect Donald Trump’s offer to be his enforcer as United Nations ambassador, The Post can reveal. The 40-year-old upstate Republican, who helped force out two Ivy League presidents with her sharp questioning on campus antisemitism, will the lead Trump’s “America first” and pro-Israel message in Turtle Bay. “I am honored to nominate Chairwoman Elise Stefanik to serve in my Cabinet as U.S. Ambassador to the United...