According to Gallup, since March, support for Democrats among whites and African-Americans has remained almost unchanged, but among Hispanics support for Congressional Democrats has been imploding. In March, Hispanics supported Democrats by a 33-point margin; that has dropped to only a 13-point margin today.

Vote for Congress, Monthly Averages by Race/Ethnicity, March-September 2010

Obviously, Hispanics have been hit hard by the economic downturn and many of them live in areas most devastated by the foreclosure crisis, but the same could be said for many whites, and there has been very little change in their level of support for the two parties.

I suspect a large amount of the loss of support for Democrats comes from their complete and total failure to deal with immigration reform. Not only did Democrats fail to pass a bill, but they never made any serious attempt. Instead, they did almost the opposite by including offensive and unnecessary anti-immigrant provisions in the new health care law that are clearly directed against Hispanics.

Political observers can argue about the feasibility of being able to pass anything related to immigrant reform over the last two years, and the super-serious beltway insiders all seemed to know nothing was going to happen, but that is clearly not what candidate Obama lead the Hispanic community to believe. Obama unequivocally promised he would pass an immigration reform bill in his first year. The truth turned out to be something quite different. Obama made no effective effort to push for immigration reform. And this broken promise does not sit well with the Hispanic media, which has been vocal in holding the president accountable.

When you promise a group of people–through their top news outlets–something very important to them, and not only fail to deliver on that promise but don’t even seem to try, it is going to result in a lot of bad blood.

I can think of little that would motivate Hispanics to turn toward an increasingly nativist, xenophobic, tea-stained Republican Party than the fact that Obama and the Democrats have so pointedly and obviously failed to deliver on promises. Democrats had a chance to lock in the Hispanic community as part of their coalition, but instead, they opted to use them and then ignore them. (Would it have really been so hard to push through the DREAM Act early in 2009?)

Let this be a lesson to politicians: There are voters out there who are still idealistic enough to think that you mean what you say; that a promise is a promise, that your word is your bond. When you seed a group’s collective hopes during the bright light of a campaign–only to crush them with the shadowy cynicism that passes for governance–don’t be surprised when you reap what you sow.