The downfall of former Rep. Randy ''Duke'' Cunningham in a bribery scandal has cleared the way for a surprisingly competitive race for his San Diego County congressional seat, a contest that will test the strength of Democratic efforts to regain control of Congress. In a poor political climate for the GOP, analysts say, a suburban coastal district of California -- even one that leans as Republican as Cunningham's -- is just the kind that could prove the leading edge of a potential national tide against the party. Yet Democratic candidate Francine Busby faces a steep uphill battle, thanks to a...