WASHINGTON -- Republican David Perdue, the Georgia businessman running for U.S. Senate, has as much as $1 million invested in an exclusive fund managed by a Swiss private bank -- a rarefied investment strategy that has earned him between $100,000 and $1 million since 2012. The fund, Vontobel Non-U.S. Equity LLC, is managed by a subsidiary of the Zurich-based private bank Vontobel to invest in companies that operate primarily outside the United States.