(nyt) AMERICAN politics has been defined by gender gaps, racial gaps, geographic gaps and the gap between the religious and the secular. Now comes the geriatric gap. As the population ages and the nation faces intense battles over rapidly rising health care and retirement costs, American politics seems increasingly divided along generational lines. The question is how real and defining this gap is going to be — whether in 10 or 20 years it will prove as consequential or intense as, say, the gender divide, particularly as it was played out last year with the presidential campaign of Hillary Rodham Clinton. As distasteful as the notion of intergenerational conflict may seem, the fight over health care — not to mention the election of health care reform’s current chief proponent, President Obama — suggests that something is going on. Older Americans are more likely to oppose Mr. Obama’s initiative than any other age group. The White House views this dynamic as one of the biggest obstacles to tamping down public concerns about its approach and assembling a legislative coalition to get a bill passed in Congress.