The implication is that the vote for the Republican is a vote that will hurt the person of a lower class--that Republican proposals and ideas favor only the rich. That Republicans will cut benefits that help those of the lower economic strata, that Republican economic theory and practice only helps those of higher incomes without benefit to anyone else.
It reeks of class conflict, this phrase. In addition, it makes voters sound selfish--like what's in this for me?
It has been said that if voters can cast votes that result in money coming to themselves that that is the "end of the republic." Voters that vote Democratic are often seen by hard core conservative Republicans as voting for continued entitlements and hand outs. This idea, mixed with latent racism, is especially applied to Black voters.
Painting with such a broad brush has a lot of hazards, one of which is indeed igniting a class war. However, the mere fact that people can apply such ideas to voters means that the idea of voters voting only in their self interest and not for the good of the country as a whole is a valid concept. This then begs the question...
When you go into the voting booth to flip the levers, put the X in the box, tap the screen, punch the card or fill in the oval, are you thinking primarily of how your vote will benefit your own self interests or those of our entire country?