问答题After eight months during which he seemed to float happily beyond the reach of his critics, George W. Bush found himself in danger of sinking last week. As clues and warnings about the Sept. 11 plot came to light and the need to assign blame grew stronger, fingers began pointing toward the White House. Bush was in an unaccustomed position — on the defensive against the Democrats, who seemed more energized than they had been in a year.This was one campaign that Bush did not delegate to others. With the cries of What did Bush know at their most hysterical, he knew better than to go out to face the cameras right away. Instead, he began behind closed doors in a Thursday lunch with Senate Republicans. Confident that his words would leak, he offered a passionate defense, saying that had he known about the plot, he would have used the whole force and fury of the United States to stop them.