147 BUENOS AIRES — Donald Trump was clear with Latin America and the Caribbean during his four-year administration — don’t do business with China. As President-elect Joe Biden readies to enter the White House on January 20, Beijing has tightened its grip over vast swathes of the resource-rich region once seen as the United States’ own political backyard. A Reuters investigation, including interviews with current and former officials and advisers, and an analysis of trade data, found that under Trump, China has left the United States trailing in terms of power and influence across most of Latin America. That poses a challenge for Biden, who has pledged to restore Washington’s role as a global leader after years of Trump’s “America First” policies, and has said that slipping U.S. influence in Latin American is a threat to national security.