Fascinating video via Ace. One guy says that the impetus for the anti-amnesty storm, from all sides of the political spectrum, is the unspoken motive of "it's cultural". It is partly cultural, for sure, which is why we often term it an "invasion."
On the other hand, the amnesty bill is purely politically-driven. With black votes securely on the Dem plantation, everybody wants to pander to the (present and future) Mexican vote, which is now of sufficient size to determine elections.