We can also link the chart to global conflict. I wouldn't so much venture it into who holds the highest political office, bit you can see trends within the political parties. Either way, the defense side of the house also collects a percentage of GDP (4% from estimates) Granted, only 3.0 to 4.4% of the GDP was spent on the Military during the Bush era. If you ask me, that's a drop in the well as far as spending is concerned.
Point: Cutting Defense spending won't help much, and will set us back further for future conflicts. Reason so much was spent post 9/11 was due to the large cuts during the Clinton time in Office. It doesn't benefit us staying behind the 8 ball in the Arms industry.