this article "the national debt graph by president" that explains how the debt got where it is

[1939]

2. A little bit oversimplified

Three things affect the size of the deficit and the growth in the national debt.:

1. Government spending

2. Tax receipts which are a function of both tax rates and taxable income generated

3. Inflation because runaway inflation (as occurred in the 1970s) trivializes the existing government debt

The big downturn in the Clinton years was largely of function of the massive capital gains generated by the stock market and the resultant taxable income spike. The initial surge in the W years was caused by a perfect storm of dotcom bust, Enron scandal, and 9-11 wiping out capital gains.

The Reagan-Bush I years and the Bush II-Obama years are times of very low inflation. Variations in taxable income (especially capital gains) seem to have more influence in the chart than do tax rates. Reagan tax cuts and Bush II tax cuts actually caused a leveling off of the growth in debt.