A measure of U.S. exports contracted for a second month, indicating a stronger dollar is making it difficult for factories to drum up overseas sales. Less investment by America’s energy producers and slower consumer spending so far this year also represent hurdles for domestic manufacturers. “There’s no question manufacturing has weakened in the past few months,” said Jim O’Sullivan, chief U.S. economist at High Frequency Economics in Valhalla, New York, who accurately forecast the ISM reading.