U.S. Congressional Demographics

Below is an interesting graphic that shows that the demographics of the U.S. population at large much more closely resembles those of congressional Democrats than those of the Republicans.  How is it possible, then, that the U.S. Senate features a GOP majority? 

Money, my friend.  The average victorious Senator spends well over $10 million on his campaign, and that kind of cash comes almost exclusively from wealthy donors, rather than from grass roots campaigns tapping the common American.