By President Obama’s own optimistic projections, American deficits will not return to what are widely considered sustainable levels over the next 10 years. In fact, in 2019 and 2020 — years after Mr. Obama has left the political scene, even if he serves two terms — they start rising again sharply, to more than 5 percent of gross domestic product. His budget draws a picture of a nation that like many American homeowners simply cannot get above water.