Thomas Nast helped bring down the crooks at Tammany Hall with cartoons. Boss Tweed, the chief antagonist of Nast, crook and leader of the Tammany Gang, understood that Nast’s drawings could do him in better than just hard hitting reporting — the pictures were clear to people who couldn’t read.
But a cartoon has to get to an audience to have an effect.
Here’s a cartoon below, a comment on the security wall being built in Israel, that got very little circulation in the west at Christmas time. Can you imagine the impact had this drawing run in newspapers in Europe, the U.S., and Canada?
It’s a mashup of a famous oil painting* related to the Christian Nativity, from a London-based artist who goes by the name Banksy. (Warning: Banksy pulls no punches; views shown are quite strong, often very funny, always provocative, generally safe for work unless you work for an authoritarian like Dick Cheney who wants no counter opinions.)

Banksy's modern nativity -- does he ever bother to copyright his stuff, or would he rather you broadcast it?
* At least I thought so in 2008. I can’t find the painting now. Anybody recognize a work underneath Banksy’s re-imagining? Let us know in comments, eh?
Tip of the old scrub brush to Peoples Geography.
More, in 2011: