US President Joe Biden and Chinese President Xi Jinping discussed Taiwan, artificial intelligence and security issues Tuesday in a call meant to demonstrate a return to regular leader-to-leader dialogue between the two powers.The call, described by National Security Council spokesman John Kirby as “candid and constructive,” was the leaders’ first conversation since their November summit in California produced renewed ties between the two nations’ militaries and a promise of enhanced cooperation on stemming the flow of deadly fentanyl and its precursors from China.