US elections always close in the popular vote
Doing some casual research about the accuracy of polls in US presidential elections, I ran across more than one site listing the results of the popular vote in presidential elections. I was surprised: in most cases, the race was close, with one candidate usually getting only a very few million more votes than the other, and often only a few thousand:
(You have to scroll half-way down this site to see the popular vote results.)
The Kennedy\Nixon election result surprised me the most. I've read reports about how voters were greatly influenced by the debates, and JFK's good looks, etc. Apparently they weren't all that influenced. Kennedy only won by about 100,000 votes.
Regardless, it seems as though the history of the results shows that the population has been split roughly in half between the left and right for a long time.