Changes in Marketable Treasury Debt Maturity 1997-2008

In the ongoing discussion of the term structure of with Calculated Risk community members PeakVT, MLM and Austin Tex the question of whether the dramatic increase in short term borrowing was a significant change or mere 'nothingburger' (paraphrase with liberties taken). I am grinding on a quarterly cumulative rollover but that might never get completed given RL demands, so I hit on an alternate route - what is the aggregate structure for the October report for as many years as electronic data is available for...The October report was taken from each year to remove any seasonality differences between years. The 1997-2008 period is used as that is the electronic dataset, there are .pdf's for earlier periods but I don't have the time (or motivation) to do the manual data grind...

Some interesting trends are apparent in the absolute amount of marketable Treasury debt in the different categories. Note in the 1997-2001 period the total US debt is declining (sigh). Also, the T Bills category is fairly constant, then both total debt and T Bills increase, then T Bills plateauing while total debt increases slowly but steadily...until this year. The rate of change for the total debt AND T Bills is nothing short of breathtaking. (NB: Y-axis scale is in USD millions, to 2008 tops out just short of $6 trillion - so far).

Also, it seemed to me a normalized view of the debt structure would be informative. Here is the percentage of the Treasury marketable debt for each component over the time series. Again, interesting trends emerge - the relative proportion of T Bills was falling in the October report 2002-2007 s total debt was steadily climbing - until 2008, with an explosion of short term debt.

(NB: The Treasury debt under consideration is the Marketable category, which the debt held by the public, other CB's etc. Hat tip to PeakVT for pointing that out. Also, some graph improvements done for today's post courtesy of Mel and Comrade Counterpointer's suggestion.)
(Addendum: MLM clarification - we are at a tipping point, some external event is needed to trigger the change from a 'status quo' approach to rollover in the Treasury market - then lookout.)