If you're not old enough to tell what Nixon was really like, then you don't have that comparison. You wouldn't suspect it was a fake without being told.

However, there are some clear give-a-ways that may or may not stick around, priming at least myself into identifying a deep fake from not: His movements do not line up with the way muscles work in the human body. In a single direction it works, but how he bounces back would cause a lot of neck strain, so no one would do that.