Nat Cohn explains in the NYT:

Why Hispanics Don’t Have a Larger Political Voice

JUNE 15, 2014

… Hispanics make up about 17 percent of the population of the United States. In the Senate races likely to determine whether Democrats or Republicans control the chamber, Hispanic voters will probably make up less than 3 percent of the electorate. …

The power of Hispanic voters is further diluted by geography. Hispanics are disproportionately concentrated in large states, like California, Florida and Texas. Incredibly, Hispanics represent an above average share of the population in only nine of the 50 states. There are very few Hispanic voters in most small states, like Wyoming or the Dakotas, and small states are overrepresented in the political process, thanks to the structure of the Senate. Effectively, the Hispanic share of the eligible Senate electorate is just 7.5 percent.

Finally, Hispanic voters are concentrated in noncompetitive states and districts, diminishing their role in the most important races. This year, Hispanics represent less than 5 percent of eligible voters in nine of the 10 most competitive Senate states, and about 4 percent of eligible voters in those races over all. That means the nation’s 50 million Hispanics have about as much say in this year’s crucial Senate races as do Alaska Natives — Native Americans in Alaska — who happen to represent 13 percent of eligible voters in the Senate’s least populous battleground.

The situation is nearly as severe in the House. Because Hispanics generally live in the same areas, Congressional map makers can easily draw heavily Hispanic and heavily Democratic districts. (Sometimes, the Voting Rights Act pushes the map makers to create such districts; sometimes neutral map makers attempt to preserve so-called communities of interest; and sometimes Republican officials deliberately draw such districts to minimize the number of Democratic seats.)

As a result, half of all Hispanics live in just 65 of the nation’s 435 congressional districts. In districts held by House Republicans, Hispanics represent only 6.7 percent of eligible voters. There are a handful of competitive House districts with a large number of Hispanic voters, making the Hispanic population share in the House battlegrounds, at 7.4 percent, slightly higher than the Senate share. But with a healthy edge in the House, the G.O.P. can afford to lose the handful of competitive seats where Hispanics represent a meaningful share of eligible voters.