Doug Stern, an Ohio firefighter who until recently was a Republican, told the Charlotte crowd that he switched parties because Republicans don't appreciate the middle class. 

"The Republican party left me, and they certainly left me as a public employee," Stern said. "Enough with the vilification of people who work for a living."

In Ohio, Gov. John Kasich (R) attempted to strip public employees of collective bargaining rights. The policy was overturned in a referendum vote last year, a major union victory among a string of defeats. Stern worked on that campaign and appeared in an ad decrying the changes, but he was a registered Republican at the time.

It's not as snappy as "you didn't build that," but people like Stern are how Democrats are rebutting the Republican message that Obama doesn't appreciate hard work.