Donald Trump is no one’s idea of a traditional Republican, but his speech Tuesday showed the rank-and-file a better way to help workers at the bottom. Democrats pound the need to raise the minimum wage, which is a tricky political issue for the GOP. “Fight for $15” fits well on a protest sign, and it’s easy to paint opponents of a higher minimum wage as heartless, even though their economic reasoning is sound.

Speaking in a Philadelphia suburb, Mr. Trump proposed a new benefit: allowing families to deduct child-care expenses...