What philosopher said that all democracies are destined to fail?

I've read variations of a view that states that a democracy is destined to fail as soon as the people begin voting benefits for themselves withour considering whether the country as a whole can afford those benefits. Author Robert Heinlein put it succinctly by saying that a democracy is doomed once people begin voting for bread and circuses. I think there was a philosopher with a more elegant way of saying it in the 17th or 18th century. I think that sage said something about a failed democracy being inevitably followed by a dictatorship. Who was that learned person and what did he or she say exactly?