WASHINGTON (AP) — Back in January 2010, President Barack Obama set a lofty goal of doubling U.S. exports in five years. Blame tepid U.S. manufacturing growth, the lingering weak global economy, and a stronger U.S. dollar, which makes it harder to sell American goods and services overseas. Monthly export numbers have been mostly stagnant this year. [...] only a scant 6,000 manufacturing jobs were added last month, according to Labor Department jobs statistics released Friday. "The goal of doubling exports keeps getting harder to achieve, not easier," said Alan Tonelson, research fellow at the U.S.