President Barack Obama congratulated French president-elect Francois Hollande for his victory Sunday, but warned of "challenges" ahead, a clear reference to Afghanistan and eurozone debt crisis. The US president was among the first world leaders to welcome Hollande's election as France's first Socialist president in nearly two decades, a result sure to have major implications for Europe as it struggles to emerge from a financial crisis. Obama invited Hollande for bilateral talks at the White House later this month ahead of a G8 leaders meeting he will host at his Camp David retreat in Maryland between May 18-19, and a...