STORY CITY, Iowa (AP) - Democratic presidential contender Barack Obama speculated Saturday that his prescription drug plan could save seniors on Medicare $157 billion over the next decade. The potential saving is proof that the nation needs to change the Medicare system, he said. "There is no reason for this other than the fact it makes the drug companies more money," said Obama. 'It's wrong that Americans have to spend more for their prescriptions because drug companies can spend billions on lobbying." The prescription drug plan pushed by Obama would allow Medicare officials to bargain for lower prescription drug prices, allow Americans to buy prescriptions from Canada and other developed countries where safe drugs are available and increase the use of generic drugs in public health programs like Medicare. Obama recently unveiled a health care proposal he said would significantly broaden coverage while also finding more than $2,000 in savings per person, largely through finding efficiencies in the system. Prescription drugs would be a key part of that, aides said. Obama aides have estimated his health care plan would cost $50 billion to $65 billion. Much of the financing would come from ending previously approved tax cuts for those earning more than $250,000 a year. On Saturday, Obama began the day by discussing his faith at a convention of the United Church of Christ, where he argued that Democrats can't concede the issue of faith to Republicans. He spoke of his faith journey, talking of "my own spiritual dilemma" where he reconnected with church as a young man in Chicago.