Shakin' the money tree
According to the Heritage Foundation, the immigration amnesty bill (if passed) woudl be pretty much the most expensive piece of legislation ever enacted by the United States government. From their report:
U.S.immigration policy should encourage high-skill immigration and strictly limit low-skill immigration. In general, government policy should limit immigration to those who will be net fiscal contributors, avoiding those who will increase poverty and impose new costs on overburdened U.S. taxpayers.
Recent proposed legislation in the Senate will do exactly the opposite. By granting amnesty to illegal immigrants (who are overwhelmingly low skilled) and creating massive new "guest worker" programs that would bring millions of additional low-skill families into the nation, such legislation, if enacted, would impose massive costs on the U.S. taxpayer.
By the time you get around to adding the costs massive influxes of unskilled immigrants add to government/society, (and remembering the current crisis in social security doesn't even take this into account), it doesn't take a genius to see that this country is headed for a major tax revolt in the not too distant future. Unless of course the politicians pushing "comprehensive" immigration reform manage to find that mythical money tree and shake a few trillion dollars out of it.