The best way to measure a president's debt is to add up
their budget deficits and compare that total to the debt level when they took office. A president's budget reveals their administration's priorities.
Note
Though they sound similar,
deficit and debt are two different things. A deficit is a budget shortfall, whereas debt is the running total of all deficits and surpluses. Deficits add to the debt, while surpluses reduce it.
President Roosevelt added the largest percentage increase to the national debt. Although he only added $236 billion, this was an increase of about 1,048% from the $22.5 billion debt level left by President Herbert Hoover before him. The Great Depression and
the New Deal contributed to FDR's yearly deficits, but the biggest cost was World War II—it added $186.3 billion to the debt between 1942 and 1945.2
President Wilson was the second-largest contributor to the debt, percentage-wise. He added about $21 billion, which was a 723% increase over the $2.9 billion debt of his predecessor. World War I contributed to the deficits that raised the national debt.2
President Reagan increased the debt by $1.86 trillion, or by 186%. Reagan's
supply-side economics didn't grow the economy enough to offset the lost revenue from its tax cuts. Reagan also increased the defense budget by 35%.2
President Bush added $5.85 trillion to the national debt
. That's a 101% increase, putting him in fourth. Bush launched the War on Terror in response to the 9/11 attacks, which led to multi-trillion-dollar spending on the War in Afghanistan and the War in Iraq. Bush also dealt with the 2001 recession and the 2008 financial crisis.2
Under President Obama, the national debt grew the most in dollar terms ($8.6 trillion)
and was fifth by percentage at 74%. Obama fought the Great Recession with an $831 billion economic stimulus package and added $858 billion through tax cuts. Even though the fiscal year 2009 budget was set by President Bush, Obama added to it with the Economic Stimulus Act in 2009.23