The zero bound on nominal interest rates is not relevant today. (It may be relevant in a deflationary environment where debt or 'safe assets' are essentially needed as a liquidity instrument akin to money, but that all gets hoovered up when interest rates rise.) The U.S. government is paying a whole lot of interest on its national debt bonds not because of a formal constraint, but rather because its bonds would go unsold otherwise, it would be unable to roll over the existing bonds as they expire, and the whole house of cards would collapse. IOW, it's the chickens coming home to roost, and the American taxpayer is paying for it. The alternative is to inflate the debt away by debasing the currency, which is even worse.