Term: 1969–1974
Richard Nixon inherited the Vietnam War and expanded the federal government's role through the creation of agencies like the EPA and OSHA. He also significantly increased Social Security benefits, indexing them to inflation, which created a large permanent financial commitment.
The U.S. economy suffered from "stagflation," leading to the 1971 "Nixon Shock" where Nixon cancelled the direct international convertibility of the U.S. dollar to gold. This effectively ended the Bretton Woods system and ushered in an era of floating exchange rates and economic uncertainty.
Debt at Start of Term (1969): ~$353.7 billion
Debt at End of Term (1974): ~$475.0 billion
Total Increase: ~$121.3 billion
Percentage Increase: ~34.3%