The president's warning against Iranian diplomats broke centuries of precedent.

By Humeyra Pamuk and Jacob BogageWASHINGTON/LUCERNE, Switzerland, June 19 (Reuters) - U.S. Vice President JD Vance is poised to take on his biggest role yet on the international…

Donald Trump said this week that, if the deal with Iran fails, he will blame J.D. Vance. He was only half-joking.