50% of the country, >90% of the productivity.
Actually, the proper percents are 80/20, also known as the Pareto Principle. ("For many events, 80% of the effects come from 20% of the causes.")
In practical reality, in most cases 80% of the productivity in any large organization comes form 20% of the workers, and vice versa. While about 50% of the country votes towards the right, that doesn't mean that they're necessarily one of the most productive members of society. If only one tenth of that productive 20% takes their assets and apply them elsewhere (Australia? Poland?), that means that America's economy loses 8%. That's about a trillion dollars or so annually, if only 2 million of the top dogs take off (not necessarily the top 10% of the productive class... only the median 10% of that productive class).