NEW YORK – As the United States takes up the decision to lift its self-imposed debt ceiling, we would do well to remember why America’s public debt is as large as it is, and how it matters. With the rise of the Tea Party, Republicans may rail against raising the debt ceiling, but they are likely to back down in the end, because, among other things, debt-funded wars – say, in Afghanistan and Iraq – are easier to defend than pay-as-you-go wars that voters must finance up front with taxes.