WASHINGTON/NEW YORK/TOKYO — Chinese President Xi Jinping and U.S. President Donald Trump are holding their second summit of the year, amid lingering tensions over tariffs, rare earth materials, artificial intelligence and other issues.After Trump traveled to Beijing in May, the venue this time is Washington. The White House has put on an elaborate show of welcoming the Chinese leader, including a state dinner. At the outset, upon Xi's arrival, the U.S. said the two sides agreed to extend their trade truce, which had been due to expire Nov. 10.But expectations for broader breakthroughs were modest, and the immediate results did…