Perhaps you’ve come across this already, but information divulged by a former senior adviser to the British government is worth considering, here across the pond:

The [reports from the Performance and Innovation Unit, Tony Blair’s Cabinet Office think-tank] were legendarily tedious within Whitehall but their big immigration report was surrounded by an unusual air of both anticipation and secrecy.
Drafts were handed out in summer 2000 only with extreme reluctance: there was a paranoia about it reaching the media.
Eventually published in January 2001, the innocuously labelled “RDS Occasional Paper no. 67”, “Migration: an economic and social analysis” focused heavily on the labour market case.
But the earlier drafts I saw also included a driving political purpose: that mass immigration was the way that the Government was going to make the UK truly multicultural.
I remember coming away from some discussions with the clear sense that the policy was intended – even if this wasn’t its main purpose – to rub the Right’s nose in diversity and render their arguments out of date.

In other words, borders were opened up both to transform the society toward the aesthetic preferences of its ruling class and to shift demographics’ role in national politics. Working- and middle-class Americans — perhaps union members, especially, given the uses to which their dues are put — should pay attention:

Ministers were very nervous about the whole thing. For despite Roche’s keenness to make her big speech and to be upfront, there was a reluctance elsewhere in government to discuss what increased immigration would mean, above all for Labour’s core white working-class vote.