DENVER (AP) _ Surrounded by an enormous, adoring crowd, Barack Obama promised a clean break from the “broken politics in Washington and the failed policies of George W. Bush” Thursday night as he embarked on the final lap of his audacious bid to become the nation’s first black president. “America, now is not the time for small plans,” the 47-year-old Democratic Illinois senator told an estimated 84,000 people packed into Invesco Field, a huge football stadium at the base of the Rocky Mountains.