WASHINGTON — Escalating the campaign warfare over the Vietnam era, a new group founded by a veteran Texas Democratic operative will announce today a television ad campaign reprising charges that President Bush failed to perform his service in the Texas Air National Guard while on temporary assignment in Alabama. The ad, funded by Texans for Truth, features Robert Mintz, a retired lieutenant colonel in the Alabama Air National Guard, who said he never saw Bush while serving in the same unit in 1972. "It would be impossible to be unseen in a unit of that size," Mintz charged in the...