Led by the oil and gas industry, this sector regularly pumps the vast majority of its campaign contributions into Republican coffers. Even as other traditionally GOP-inclined industries have shifted somewhat to the left, this sector has remained rock-solid red.

Since the 1990 election cycle, more than two-thirds of this sector's contributions to candidates and party committees has gone to Republicans. Besides oil and gas, the electric utilities industry is another big donor in this sector. Less generous, but even more partisan, is the mining industry. [Read more Background]