definition 1: to punish or humiliate by coating with tar and feathers.
definition 2: to punish with vicious criticism.
The politician pictured below has been tarred and feathered in effigy. Tarring and feathering is a most public form of punishment and humiliation.
A politician tarred and feathered in effigy
Actual punishment using tar and feathers varied in viciousness, depending on the type of tar, its melting temperature, and where on the victim’s body it was applied. As with “keelhaul,” those with a penchant for horror and history will find lots of information online. As an expression (definition 2), “tar and feather” is fairly common and sometimes accompanied by “and ride him out of town on a rail.” This rail is yet another type of cruel and unusual, publicly humiliating punishment. This combo–of tar, feathers, and rail–is depicted in a scene at the beginning of the movie John Adams.
Writers, however, should be aware that “tar and feather” could be considered a punishable cliche, what George Orwell in Politics and the English Language calls a “dying metaphor.” But this is such a big topic that it will have to wait.