Obama: World Leaders Rattled by Possible Trump PresidencyPresident Barack Obama says world leaders he has spoken with are "rattled" by the presence of Donald Trump as a candidate in the 2016 presidential race - and offered his own harsh criticism of the bombastic billionaire. Speaking to reporters in the coastal Japanese city of Ise Shima Thursday, after the first day of an annual summit of leaders of the world's seven wealthiest nations, the president says the world is paying close attention because "the United States is at the heart of the international order." Trump has dominated the race for the Republican presidential nomination based on his controversial statements about hispanic immigrants and Muslims. He has also called for withdrawing U.S. forces from Japan and South Korea and arming those countries with nuclear weapons to counter the threat from North Korea. Obama says his fellow leaders are "not sure how seriously to take some of [Trump's] pronouncements," which "display either ignorance of world affairs, or a cavalier attitude, or an interest in getting tweets and headlines." Economic woes\n\nThe U.S. president says he and the other G7 leaders discussed the challenges facing the global economy on the first day of the summit, and ways to "sustain the momentum of the recovery that's taking place in the United States." Japanese Prime Minister Shinzo Abe presented a grimmer view of the global economy, comparing current economic conditions with those of 2008, when the collapse of U.S. investment bank Lehman Brothers triggered a global economic recession. Many observers believe Abe was making those comparisons to give him cover for delaying a planned increase in Japan's consumption tax. Terrorism, maritime security \n\nFriday's agenda at the G7 will include combating terrorism and maritime security. The last point is an obvious nod to China's increasing territorial expansion in the resource-rich South China Sea, in the face of rival claims by its Asia-Pacific neighbors. After the summit, Obama will travel to Hiroshima, where tens of thousands of Japanese were killed when a U.S. warplane dropped the world's first atomic bomb in 1945, hastening the end of World War II.