Ukrainian forces have yet to set up defensive lines as they continue their operation into the Kursk region of Russia, a U.S. official told ABC News on Wednesday.While this might reflect Ukrainian confidence in further success for the offensive, there is concern among some American officials that failure to dig in soon could leave its troops vulnerable to a coming Russian counterattack."Russia didn't take it very serious at first," the U.S. official said. On Tuesday, Pentagon spokesman Maj. Gen. Pat Ryder said the U.S. had seen only a "small number" of Russian forces heading to Kursk.But the U.S. now sees...