Lexicon of Politics

October Surprise n. the release of important news in the month before election, in hopes of affecting the outcome, esp. by an incumbent.

1980 New York Times (Sept. 1) A7:
Republicans worry about an "October Surprise" in foreign policy.

2003 Seattle Times (Nov. 29):
The phrase "October Surprise" has become a part of the political-campaign lexicon, the notion that an incumbent president can make some major announcement or take some substantial action in the monthlong run-up to Election Day.