Rep. Elise Stefanik withdraws bid for U.N. ambassadorship, Columbia University's interim president resigns, and Iran signals openness to 'indirect' nuclear talks. President Trump nominates Mike Waltz as U.N. ambassador. Former national security advisor Mike Waltz tapped after being ousted from National Security Council. Several names floated for U.N. ambassador role after Stefanik withdrawal. Trump emphasizes need for historic tax cuts, great jobs, record economic growth, secure border, and energy dominance.