Hi doma,
May I suggest you check Erin's derived numbers against the absolute ones provided by the Treasury.
http://www.treasury.gov/resource-center/data-chart-center/tic/Documents/mfh.txt
and the GAO
http://www.gao.gov/special.pubs/longterm/debt/debtbasics.html#largefeddebt
Here's a list of total debt with history provided by the Whitehouse (see Table 7 on page 144of 36
http://www.whitehouse.gov/sites/default/files/omb/budget/fy2013/assets/hist.pdf
Here's a chart showing the accumulation of US debt by foreign holders over time.
http://en.wikipedia.org/wiki/File:Composition_of_U.S._Long-Term_Treasury_Debt_2005-2010.PNG
As a general rule of historical research, it really pays to check original sources rather than to base one's opinions on intermediaries.
Then you can make your argument using the actual numbers.