Which president ran up the biggest US national debt?

US Federal Debt 1980-Present -- Increase by President

Ronald Reagan increased US national debt by $1.9 trillion. That represented 11.3% of US GDP in his first term and 9.3% in his second.

George H.W. Bush, by $1.5 trillion, or 13% of US GDP

Bill Clinton, by $1.4 trillion or a decrease of 0.7% of GDP in his first term and a further decrease of 9% in his second.

George W. Bush increased debt by $6.4 trillion. That represents a rise of 7.1% against GDP in his first terms and 20.7% in his second.

Barack Obama is currently on a $2.4 trillion increase. That represent a rise of 9% as a proportion of GDP.