Every database works a little differently, but here are some general tips that can help you locate political cartoons in the ProQuest newspaper databases (Historical New York Times, Baltimore Sun, etc.):
You can try searching these databases to find political cartoons that have been published in newspapers.
In the databases, make sure you are on the "Advanced Search" screen, then under "Document type," click on the check box next to "Editorial Cartoon" Click on "Search" to see all cartoons, or add a subject term in the search boxes above.