WASHINGTON (Reuters) - President Bush and Democratic Sen. John Kerry are tied nationwide in a tense race for the White House, but Kerry leads in six of 10 battleground states, according to Reuters/Zogby polls released on Sunday. Kerry and Bush were deadlocked at 48 percent in the latest three-day national tracking poll, which included one day of polling taken after the airing of a videotape from Osama bin Laden. Kerry led Bush 47 percent to 46 percent on Saturday. Only 2 percent of voters remain undecided as Bush and Kerry scoured about 10 remaining battleground states to find the 270...