The phenomenon is a bit like running up the down escalator. Without interest payments, the president’s plan would balance the budget by 2017. But net interest payments that year are expected to reach $627 billion, up from $207 billion in the current fiscal year.

“This goes to the heart of why we have to address our fiscal problems,” said Mark Zandi, co-founder and chief economist at Moody’s Economy.com. “If we don’t, we’re going to get swamped by our interest payments.”…

Even with the cuts in Obama’s budget, relief would not come until 2021, when the deficit as a percentage of gross domestic product would stop rising and plateau at 3.4 percent.