WASHINGTON (Reuters) - U.S. Senate Democrats turned up the heat on the White House on Friday to act in the face of record-high U.S gasoline pump prices. The same day, the Senate Energy Committee set a September 8 hearing on what's behind the prices, which hit a record $2.55 a gallon this week. That's about 68 cents higher than just a year ago and the biggest weekly increase on record, which has triggered fears that high energy costs could hurt U.S. economic growth. Lawmakers admit there is no short-term fix to pain at the pump, but are nervous about political...