Contemporary third-party confirmation that the U.S. Government never repays the principal amount of any loan of credit (belief, trust) from the Federal Reserve, and only makes payments of interest.

“The nation’s credit rating is at risk if the $19.9-trillion debt limit is not raised ‘in a timely manner’ before the Treasury runs out of cash in October, Fitch Ratings warned on Wednesday.
“. . . But Moody’s said it believed that the Treasury could prioritize interest payments on the federal debt ‘to preserve the full faith and credit of the U.S. government and to avoid disruption of the financial markets’ if the limit is not raised before then.” Los Angeles Times, “U.S. credit rating at risk if debt limit is not raised in a 'timely manner,' Fitch warns,” http://www.latimes.com/business/la-fi-debt-limit-fitch-20170823-story.html.

Notice that “the full faith and credit of the U.S. government” depends only on interest payments.

The national / federal debt owed by the U.S. Government to the private Federal Reserve for the loan of costless digits of credit is the anvil that will wears out every hammer of production in America and ensures that the government is the slave in the relationship and the Federal Reserve the master.