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.