A “stemwinder” is a rousing political speech that galvanizes a crowd to take action.
The Word Detective notes the term is “one of those grand old words that have traveled so far from their origins that nearly all traces of their beginnings have faded from popular culture.”
Slate: “The term dates back to the middle of the 19th century, when the stem-winding watch came into vogue. The newfangled timepiece was a vast improvement over its predecessor, the key-wound watch, because the mechanism for setting it was a stem actually attached to the watch, rather than a key that was easily and frequently misplaced. This technological advance was so widely appreciated that, by the end of the 1800s, the term stemwinder had taken on the figurative meaning of ‘excellent’ or ‘outstanding,’ or, as the Oxford English Dictionary puts it, ‘a person or thing that is first rate. …'”