The government borrows by selling mostly long-term bonds with an interest rate of around 4% to 5%. The government should borrow by selling more short-term bonds with an interest rate of 0.25% to 2%. Paying 2% instead of 4% on a $14 trillion debt would save $280 billion per year.
For every 100 basis point increase in interest rates, the interest on the $14 trillion debt increases by $140 billion. Flirting with the disaster that would be caused by a default results in less confidence by investors on the risk of Treasury securities, increasing interest rates.