WASHINGTON, July 23 - During his campaign for the presidency in 2000, George W. Bush took a dramatic step: a vow to support the ban on assault weapons, enacted in 1994 for a 10-year period. "It makes no sense for assault weapons to be around our society," Mr. Bush declared. Since then, the president's advisers have repeatedly affirmed his support for the ban, a position that has helped him appeal to moderate voters and demonstrate independence from the powerful gun lobby. But in the middle of a presidential election year, and with only five working days left in Congress before...