Election surprise
An election surprise (also a pre-election surprise, or, in the U.S., October surprise, where elections are held on the first Tuesday after the first Monday of November) is an event which occurs preceding an election which has enough shock value that it may be able to sway voters in close elections. When planned, an election surprise may be an act of propaganda. Election surprises typically fall into categories such as terrorism, political scandals, etc. There may be disagreement as to what constitutes an election surprise for several reasons:

There may be general disagreement as to whether the event in question affected, or was intended to affect the outcome of the election, especially as the event and the election may occur in different countries. There may be a lack of consensus as to which party the election surprise may have helped, or was intended to help.