Always look for the "cheap labor" angle in Republican/neocon operations, they're all about making labor as cheap as possible so the owning class can skim more off the top. Racism and nationalism are tools in achieving these ends, providing sideshow material to motivate bigoted voters as well as neutralizing their natural opposition. Watch where the money goes as a result of their policies, and you'll find a cheap labor conservative holding the bag every damn time.
I first turned on to this thanks to an article on Conceptual Guerrilla a few years ago. CG frequently uses cheap labor as a basis for successfully deconstructing neocon ideology:
http://www.conceptualguerilla.com/In this case, the cheap labor the cons are smacking down is the migrant agro-worker population. However I think the underlying motive is turnout of the anti-immigrant base. They'll have to be careful how they play this, cos they want to avoid smearing their frozen peas magnate/incumbent senator at the same time. Putting this on the ballot for November is a risk, strangely enough, and it could easily backfire in Smith's direction. Given all that, I'm inclined to think this is part of a coordinated national campaign by the Heritage foundation and its close allies with only the presidential race in mind, rather than a home-grown movement. Look for similarly-worded measures in other swing states that allow petition-driven ballot referendums.