Despite two decades of dire health warnings and threats of federal intervention, the specialty drugmakers have repeatedly staved off tougher federal oversight with the help of powerful allies in Congress. Over the years, industry friends like Tom DeLay, the former House Republican leader from Texas, have come to its defense. Even Senator Edward M. Kennedy, regarded as the strongest healthcare advocate in Congress in recent times, dropped efforts to impose new safeguards. The pharmacists known as compounders are now facing their biggest regulatory threat as they confront questions at Congressional hearings on the deadly outbreak. The question is whether Congress will move to oversee the niche industry more aggressively.