No the debt has never went down. The debt as a fraction to GDP has went down but not the debt.
The debt is too great to fix and we will go under as a nation.
Did you even look at the chart? It's total gross debt as well as debt:GDP ratio.
You can clearly see the debt is in decline after WWII, during the 1950's and at the tail end of the 1990's. If you do not see this, then I am assuming you have problems with your eyesight and/or reading comprehension.