The president seems to have a case of Potomac Fever. It's another weekend in Washington for President Bush, who in the past has tried to get away any time he can to his Texas ranch or Camp David. But his last trip to the presidential retreat came during a driving snowstorm last month, leading him to put off more visits. It's not like the White House is such a bad place to stay. President Reagan called it an eight-star hotel, with doting staff, good food, and a movie theater. The president's weekends in town are mostly spent doing work, exercising and relaxing -- while entertaining friends at night in the mansion. It's not as good a deal for much of his staff, who would have a weekend off if he left town.