I was easily able to tell who Nick was on that ER episode, mostly because their eyes were identical. His father looked much older and a little thinner than Nick does now, his mustache was not as prominent. You could definitely tell that they were related. His father had facial hair, but not nearly as well groomed.

It isn't surprising that Nick Offerman knows so much about US history. His father taught my 8th grade U.S. History class. When Nick was going to be in the live episode of E.R., the principal made a big announcement about it and encouraged us to watch.