This term came from a Massachusetts congressman who wanted to demonstrate what would happen if the former Confederate states (who were basically the Democrats) regained power within the government. The shirt he waved around belonged to a carpetbagger who was flogged in Mississippi. It was supposed to remind everyone who was responsible for the Civil War and that the Democrats would dismantle all the work done with the Reconstruction.

It came into popular use by Republicans who wanted to obscure a partisan issue. It worked so well that many relatively honest Republicans would use it in campaigning and to discredit Democratic proposals. This was also a powerful appeal and reminder to any Black voters who showed sympathy towards a Democratic candidate of who was responsible for instituting slavery. It worked for a surprisingly long time. If you waved the bloody shirt you got your way.

The Union veterans also used this tactic (probably with more right since it was their symbolic blood staining the proverbial shirt) to argue for veterans' pensions. The leaders of the Grand Army of the Republic referred to this many times while trying to persuade the Republicans to enact benefits for those disabled during the war.