CARTAGENA, Colombia - President Barack Obama's challenge during a weekend summit in Colombia with business executives and political leaders from the Americas is convincing US business that he's serious about expanding trade in Latin America and persuading the region to look northward once again. "Put simply, we have one of the world's most dynamic trade relationships," he planned to tell CEOs on Saturday during the sixth Summit of the Americas. But playing the persuader is not an easy task. The U.S. faces trade competition from China, resistance from labor at home, a set of difficult regional issues that could dilute any focus on trade, and now the distraction of Secret Service agents in Cartagena relieved of duty on allegations of misconduct. The business session was expected to include executives from Wal-Mart Stores Inc., PepsiCo, Yahoo and Caterpillar. "Here in Latin America, the U.S. is the largest foreign investor, and we're the largest customer of manufactured goods from countries across the hemisphere," according to Obama's remarks released in advance by released by the White House. While US exports in dollar amounts have increased in the Americas, its share of the market has declined over the past decade. China, in particular, is surpassing the U.S as a trading partner with Brazil, Chile, and Peru. In the United States, labor is restive over a trade deal with Colombia that is awaiting final certification. The Colombian government has worked to meet the requirements of a labor rights agreement that was a condition of passage in Congress last year. The question in Cartagena was whether Obama, over the objections of U.S. union leaders, would certify that Colombia successfully has met the terms. US Chamber of Commerce President Tom Donohue said in an interview Saturday that even if Obama did not take that step while in Cartagena, a final certification probably would come soon. He said Obama may not make a major announcement so as not to irritate allies who oppose the deal.