I know it's been a few weeks since they came out, and this is a bit of "old news", but the hundreds of pages of Russell Pearce's bigoted emails are still turning up nuggets. In this case, he is thoroughly willing to misuse quotes and science to serve his bigoted ends.
To whit: on page 20 of the linked .pdf file, Pearce quotes a Democrat, President Harry S. Truman -
I think that the line was actually first used in the 1948 presidential campaign, but to be fair to Pearce, that issue of Look magazine may have contained an interview or quote from Truman. Given that Pearce was born in 1947 (or so says his Wikipedia bio), he was probably too young in 1948 to pay attention to presidential candidates, and by 1956, if he was soaking up wisdom at the (metphorical) knee of any "Democrat", it was probably Bull Connor.
But whether it was 1948 or 1956, either way, Truman wasn't talking about immigration or immigrants.
To whit2: On page 45 of the same file, Pearce forwarded material that admits the reality of global warming and other environmental concerns, matters that Republican orthodoxy either minimizes or calls an outright hoax -
Now, it seems as if the phenomena cited were meant to serve as points arguing against all immigration (not just the undocumented variety that Pearce claims is all that he is concerned with), but hey, it's a start. :)