WASHINGTON (Reuters) - A "phase one" trade deal between the United States and China was supposed to be a limited agreement that would allow leaders from both countries to claim an easy victory while soothing financial markets.But it may morph into something bigger if U.S. President Donald Trump agrees to Beijing's demands to roll back existing tariffs on Chinese goods, people familiar with the talks say.China's commerce ministry said this month that removing tariffs imposed during the trade war..