You also need to ask why the GOP has been so reluctant to actually do anything after all those years. Much of the speaking out against illegal immigration by politicians has been mere rhetoric, it seems. With the GOP leadership, it was all a façade. They had to be aware that the border patrol was ridiculously underfunded, and department policies had been put in place making it nearly impossible for Immigration Enforcement to do their job. For decades they were reluctant to go after the employers of illegal labor, even though there was blatant disregard for the law.

The truth is that many Republicans bought into the Liberal economists telling them that immigration was good for the economy. We can see this culminating with George W. Bush saying that immigrants are doing jobs Americans don't want to do.
http://www.csmonitor.com/Commentary/...8s01-comv.html