As September comes to an end, presidential-election observers are beginning to wonder if there will be an October Surprise. In a campaign where the unexpected has become normalized, both parties -- but particularly Democrats -- suspect that the next month could bring a shocking revelation.

The notion of an October Surprise gained widespread popularity in the 1980 election, when Ronald Reagan's campaign feared that President Jimmy Carter would announce a resolution to the Iran hostage crisis only weeks or days before Americans went to vote. While Carter was in fact working on an end to the crisis, irrespective of the election, the Iranians did not release the hostages until after Reagan's inauguration.

On the rare occasions when October Surprises have happened, they have not really impacted the outcome of the election. In 1956, Egyptian President Gamal Abdel Nassar nationalized the Suez Canal and the Soviets invaded Hungary shortly before the election. The crises, and Eisenhower's responses, were not determining factors in the president's landslide victory against Adlai Stevenson. He was well on his way to victory before either crisis broke. 

In October 1964, one of President Lyndon Johnson's closest and most trusted aides, Walter Jenkins, was arrested in a Washington YMCA for engaging in sexual acts with a man. Though Johnson feared the arrest would hurt his campaign, Johnson went on to enjoy a landslide victory against Republican Barry Goldwater. 

The most dramatic incarnation of a political surprise took place in 1968. On October 31, Johnson announced that he would undertake an immediate bombing halt against the North Vietnamese in the hope of reaching a peace agreement. The announcement sent shudders up the spine of Republican Richard Nixon, whose campaign had promised that as president he would bring peace. Some people in his campaign were so worried they attempted to scuttle a settlement by promising the South Vietnamese a better deal if Nixon became president. Nixon, though, went on to win. ...