WASHINGTON — U.S. President Donald Trump on Thursday startled Japan's prime minister by mentioning the 1941 attack on Pearl Harbor, a seemingly light-hearted remark sure to elicit unease in a country now a firm U.S. ally. Trump, in a notably friendly meeting with Prime Minister Sanae Takaichi, spoke to reporters about why he did not notify allies before the United States and Israel attacked Iran on February 28. "We didn't tell anybody about it because we wanted surprise. Who knows better about surprise than Japan, OK?" Trump said in the Oval Office. Looking to Takaichi, the 79-year-old president said, "Why didn't you tell me about Pearl Harbor, OK?" Takaichi, who was relying on an interpreter, did not say anything but appeared to hold back a slight sigh as she shifted in her chair, with at least one audible groan heard in the room crowded with U.S. and Japanese reporters. Imperial Japan launched a pre-emptive attack on the key U.S. Pacific base in Pearl Harbor, Hawaii, on December 7, 1941, hoping to strike a decisive blow before an expected U.S. entry into World War II. More than 2,400 A