Noting that Sarkozy's polling lead over Royal in France is considered a "large margin", the blog (new to me) Dr. Charlemagne's Woes posits an intriguing theory: "The 50/50 rule."
It has to do with the scientific concept of a "steady-state." This phenominon is frequently encountered in chemistry. For example, the evaporation of water into a closed space. What happens is that water molecules leave the liquid phase for the gas phase until there are so many gas molecules floating around that every time one tries to leap into the gas, another has landed in the liquid. While many of the individual molecules may change their state over and over again, the number in each state reaches an equilibrium.
As similar kind of phenominon is observed in social systems such as the stock market. The famous Chicago School efficient market theorists showed, essentially, how natural markets can efficiently find the exact price of something for a given set of conditions. Change a condition and the price is disturbed, bounces around in a kind of damped oscillation, and then finds the new price. Indeed, Wall Street has been hiring the likes of Physical Chemists to help them develop option trading strategies.
So, now consider the old see-saw between the Left and the Right. Imagine that a swing percentage of voters changes from one side to the other in proportion to prevailing conditions. In this case the conditions are not temperature and pressure, but law, policy, and maybe even interest rates. When things get pushed too far one way or the other on any of the perpetual Gordian knot type of issues, a freely functioning democracy will elect policy maker that corrects the disturbance. When efficient markets are disturbed buying and selling restores temporarily [aberrant] pricing; when efficient democracies are disturbed, electing and unelecting correct [aberrant] policy.
This brings us to the 50/50 rule. Consider the perpetually debated issues with all of their encompased grey areas. Any of the traditional unanswered (or unanswerable) questions of the American body politic (classically, abortion). Here we find a 50/50 deadlock. Despite the complexities of the arguments, the grey areas like partial birth abortion, and the embarassing zealots on either side, the country is split, evenly. To my eye this probably means two things: 1) That current policy is about right and 2) that our democracy has functioned efficiently on this issue. Were the law to be changed dramatically one way or the other, public opinion would shift heavily against the temporarily prevailing side until elections and unelections of law and policy makers fixed the percieved error, restored the equilibrium.
I am far from persuaded, but there may be a kernel of truth here. One of those concepts to play with. It implies that Americans do not really want much change at all, and panic when in effect when serious change looms.