Did you look at the graph?

Eisenhower had two terms = 8 years - did poorly.

Kennedy + Johnson two Democratic terms in a row = 8 years, did well.

Nixon + Ford, two Republican in row = 8 years, did poorly.

Carter 1 term, did well.

Reagan Bush - 3 terms Republicans 12 years, did poorly.

Clinton 2 terms 8 years did well.

Bush the second, 2 terms 8 years did poorly.

Obama 2 terms 8 years did well.

Trump, 1 term did extremely poorly

Biden 1 term did well.

So this 4 years thing you're talking about you mean that we can't be sure about Biden, Trump, or Carter. Fair enough, is the 8 years good enough or is that also too short to draw a conclusion?