You're leaving out the "by force and violence" part of the statute. Not too many Americans point loaded weapons at Census agents.
There's a WHOLE RAFT of ways you can "impede" a "Federal official", and it doesn't have to be by force and violence.
And there's a WHOLE RAFT of "Federal officials", as you can see in my post #49.
You're aware that there's a lot of sections of U.S. Code 18?