President Obama's announcement this weekend that he was backtracking on his pledge to reform immigration policies  by the end of the summer was quickly attacked by advocates, Republicans, and members of his own party. House Speaker John Boehner said that the decision "smacks of raw politics" -- which is both somewhat ironic and almost certainly true.

One problem that the president and Democrats face is that Hispanic voters are much less likely to vote than other demographic groups -- and that's especially true of voters in the states that will determine whether or not Democrats hold the Senate.

The Census Bureau collects data on voter turnout by demographic group and state. It's not perfect data, but it provides one of the better year-over-year comparisons between how different racial groups vote.

In short, Hispanic citizens consistently vote at lower rates than white non-Hispanic or black citizens. If we assume, however crassly, that Hispanic voters are those most likely to support Obama taking unilateral action on immigration, that voting reality is a key political consideration.

As the graph below notes, turnout among whites in mid-term elections -- which are almost always lower-turnout elections than presidential ones -- is roughly equal to turnout among Hispanics in presidential races.

turnout

That trend is clearly visible when you compare turnout in 2010 with turnout in 2012. The chart below shows the percent decrease in turnout rates between 2012 and 2010 for the states with the country's largest Hispanic populations. Toggle between white and Hispanic; in nearly every case, the drop-off among Hispanic voters was substantially higher than that for whites.

Now here's the kicker: notice that none of those states have hotly contested Senate races this year. Looking at the races most commonly considered toss-ups -- Alaska, Arkansas, Colorado, Georgia, Iowa, Kentucky, Louisiana, Michigan, and North Carolina -- a different pattern emerges. In Colorado, Hispanic turnout was 39 percent lower in 2010 than 2012. In Michigan, 43.5 percent lower. In Georgia? Fifty percent. (In every other state besides North Carolina, there wasn't enough data on Hispanic voters for the Census Bureau to evaluate turnout with accuracy.)

Obama's political calculus was simple. In the states he -- or, more accurately, his party, is most worried about this fall, taking action on immigration almost certainly wouldn't be rewarded with more votes. Everywhere else, the gap between white and Hispanic turnout is likely to be even larger than it was two years ago.

The thing about politics is that, at its heart, it's all math. And the math was against reform in 2014.