President Obama and his allies, concerned about deep skepticism over his landmark health care overhaul, are orchestrating an elaborate campaign to sell the public on the law, including a new tax-exempt group that will spend millions of dollars on advertising to beat back attacks on the measure and Democrats who voted for it. Americans will see the first evidence of the public relations offensive on Tuesday, when Mr. Obama travels to Wheaton, Md., to conduct a nationally televised question-and-answer session with older citizens to trumpet one of the law's most popular features: $250 rebate checks to help Medicare beneficiaries pay...