Micah,
Off the top of my head, I can think of four plausible answers to that question, none of which are mutually exclusive:
- Santorum and Huckabee’s policies wouldn’t necessarily benefit blue-collar voters, so there’s no natural allegiance there.
- The GOP has become a highly ideological party; even blue-collar Republican voters principally put ideological and cultural concerns above economic concerns, and other candidates speak to those better than Santorum and Huckabee.
- Blue-collar voters within the GOP feel disenfranchised by the Republican establishment, so candidates like Trump have more appeal to them.
- Santorum and Huckabee are old news. Maybe they are overperforming among blue-collar voters — but that could mean getting 4 percent of the vote instead of 2 percent.