For over two hundred years, whenever a debate has broken out in the United States, political cartoons have been there to take part in the argument—and sometimes to push it to its limits. Beginning in 1754, when Benjamin Franklin’s “Join or Die” cartoon appeared in the Pennsylvania Gazette, political cartoonists have long used their skills to praise, attack, caricature, lampoon, and otherwise express their opinions on the most urgent political issues of the day. Political cartoons began as a street-level phenomenon. In the late eighteenth and early nineteenth centuries, they were often posted on walls or passed from person to...