Greg is right. Our immigration system does not work, and much of our economy relies on "illegal" immigrants. Without them, our agricultural industry fails. He's also right that the majority of those immigrants hold beliefs and values that are compatible with what the republican party espouses: religion, family values, etc. I've made this point before, probably in this thread. That being the case, I wonder why the republican party doesn't embrace this potential conservative voting block? What could it possibly be?
The even more cynical take is that the democrats recognize this dynamic. They know that the hope of immigration reform keeps those votes rolling in, and that once reform passes they won't maintain that advantage (which is slipping anyway). So, the democrats aren't actually serious about reform because they will lose their carrot. It's all fucked.