This is why the US should not worry about China as a long-term economic threat - authoritarianism has never worked. The Soviet Union, 1930s Germany and Italy, all collapsed. I think the Chinese realize this and are pessemistic about their own future. The Constitution was designed to make the US Government as weak as possible, because a strong government ultimately turns on its people.
Neither has democracy, depending on the definition of "worked". Try to narrow it down.
> The Constitution was designed to make the US Government as weak as possible
That is a premise, not a truism. Every democracy has, in time, given in to an appeal by the masses to (either by dupe or passively) give the government more power until it's not relatively weak.