[yellowapple]

Because not all presidents have served for two full terms. Examining things while ignoring the time period over which they happened does not a meaningful analysis make.

[kelnos]

In that case, neither metric is appropriate, and we should be looking for the trend per presidential term.

[yellowapple]

O(year) ≈ O(term) / 4

(Assuming that all terms are the full 4 years long, which happens to be the case for all of the presidents being discussed in this thread)