Terry O'Sullivan, general president of the Laborers' International Union of North America, said a Romney presidency would be "disastrous" and that concerns over potential policy changes "are already resonating in the trenches." Noted Dennis Crane, business agent at sheet-metal workers' union Local 7 in Portage, Mich., "The Republicans are acting like idiots. Our guys are pissed off, and they are anxious to get out and vote."

Ed Knox, president of electrical workers' union Local 68 in Denver, predicted that Obama "may see even more support this time around than last time" from union members.

That's welcome news for construction unions heading into the November elections. In 2008, the AFL-CIO dedicated unprecedented resources toward its get-out-the-vote efforts. McGarvey predicts the umbrella union organization will allocate at least as much toward the 2012 election, trying its best to match up against well-funded Republican super PACs.

"We can't compete on dollars," McGarvey said. "For us, it's one-on-one, shoes-on-the-street conversations with our members, their families and friends. That's more valuable than some billionaire's ad on TV."