Are you intending to claim that the second half of the 20th century isn't contemporary?

I'm not a historian, but I've understood "contemporary" as a term that refers to events that have occurred in the lifetimes of active historians. Given that a decent chunk of the US's population was alive in 1968 and hasn't even retired yet, it probably fits neatly into that category.

Right, see here: https://en.wikipedia.org/wiki/Contemporary_history

"[..] a subset of modern history that describes the historical period from approximately 1945 to the present."