The problem here is that Immigration has become such an issue because it is being used as a multipronged attack directly upon Every American. Between the use of Illegal labor, Imported labor (H1 & L1 visa), and moving our jobs to other countries altogether, the three fronts are destroying job/income opportunities for the largely unskilled workforce in America. High paying jobs are being destroyed or exported then replaced by lower paying jobs. The wage on the lower paying jobs is further driven down by the presence of illegals. Bush, via trade and immigration policy, has fostered the utter subversion of the US economic system for the profit of a few. But, Immigration also sits in the national security camp for some, which grows the level of outrage.
How one can sit and ask "why" this is an issue is so out of touch as to need their head examined. On the other hand, the politicians seem to sit squarely in that camp. They also don't get why they're losing their base on both sides of the isle. This is called "ripeness" for a third party bid. You get a third party in there saying publically what I just said and they'll landslide it.
"We did this...once before, in 1992, didn’t we? How’d that work out for you?"