Denny, you're doing an admirable job trying to explain that table, but it's kind of hard to argue against (people can disagree with me about it and that's fine.)
Assume (just for fun, even if you're hard to the right) it's pretty accurate to the way spending changes during D and R presidencies. I know it's a hard stretch for some of you lol, but if you make that assumption, then how do you explain it? One theory might be that the D's have a reputation for being free spenders and they don't like it. On the other hand, R's have a reputation for cutting spending that they generally like.
If that's true, then when a D is president they're doing what they can to prove the reputation wrong while the R's are hopping up on their soapbox talking about how good they are at cutting spending. In other words, they're both pre-disposed in the same direction of cutting expenses.
On the other hand, when an R president is in power, they're not trying to prove anything about spending and they run up the bill. The D's don't have as much of a dog in the fight and go along for the ride. Spending goes up.
Pretty much impossible to prove one way or another, but it's interesting to think about.