Well, Ted Cruz has won Iowa, an outcome I find about as frightening as a Trump victory. A few days ago, a disturbing report surfaced about Trump making inroads among union members. According to a study conducted by Working America, white working-class voters who support Trump cited his tendency to "speak his mind" as the quality they most admired.
Possibly the biggest blow to labor under a Trump or Cruz presidency would come in the form of extremist Supreme Court nominees. With unions already under assault at the state level, a Supreme Court even more opposed to worker rights would be absolutely devastating.