Interest rates aren’t falling, and with the U.S. debt-to-GDP ratio projected to reach 115 percent over the next decade, the situation becomes ever more dire.

 Covering the topic of "Public debt and low interest rates," Blanchard argued that because interest rates were so low, developed economies did not need to worry too much about debt.

So long as the economy grew at a faster pace than real interest rates, which were then about zero, governments could spend more.

The 0 percent rates that we saw in the decade after the financial crisis may have been a fluke, the result of decades of low and predictable inflation, as well as unlimited demand for U.S. bonds relative to their supply.

Even if the Federal Reserve starts cutting rates soon, real ten-year rates may settle at 2 percent or 3 percent going forward.

Any benefit of extending the government's debt maturity was largely undone by quantitative easing, in which the Federal Reserve bought long-term debt by issuing short-term liabilities to banks.

High rates can become a vicious circle, as a hike in rates further increases debt, which pushes rates up even higher as more debt gets issued.

High debt levels can make the public nervous about inflation-creating another vicious circle, as higher expected inflation pushes up interest rates and puts pressure on the Fed to be more hawkish. 

https://www.city-journal.org/article/our-unsustainable-debt