Could there be a real October Surprise?_00005425.jpg
PHOTO: Getty Images
Could there be a real October Surprise?_00005425.jpg
Now playing
02:44
Could there be a real October Surprise?
PHOTO: TV3
Now playing
01:01
Clinton: Children treated as political pawns
AUSTIN, TX - NOVEMBER 17:  Former U.S. Secretary of State Hillary Rodham Clinton signs copies of her new book
PHOTO: Rick Kern/WireImage/WireImage
AUSTIN, TX - NOVEMBER 17: Former U.S. Secretary of State Hillary Rodham Clinton signs copies of her new book 'What Happened' at BookPeople on November 17, 2017 in Austin, Texas. (Photo by Rick Kern/WireImage)
Now playing
01:01
Hillary Clinton: That is an outright lie
Bill Clinton CBS Sunay Morning
PHOTO: cbs
Bill Clinton CBS Sunay Morning
Now playing
01:32
Bill Clinton reflects on Trump media coverage
President Donald Trump speaks at a rally at the Gaylord Opryland Resort and Convention Center, Tuesday, May 29, 2018, in Nashville, Tenn. (AP Photo/Andrew Harnik)
PHOTO: Andrew Harnik/AP
President Donald Trump speaks at a rally at the Gaylord Opryland Resort and Convention Center, Tuesday, May 29, 2018, in Nashville, Tenn. (AP Photo/Andrew Harnik)
Now playing
01:06
Trump: I drew in bigger crowds than Jay-Z
PHOTO: Getty Images
Now playing
01:34
Chelsea Clinton slams Ivanka over Trump support
PHOTO: CNNI
Now playing
01:39
Hillary Clinton trolls Trump with Russian hat
AUSTIN, TX - NOVEMBER 17:  Former U.S. Secretary of State Hillary Rodham Clinton signs copies of her new book
PHOTO: Rick Kern/WireImage/WireImage
AUSTIN, TX - NOVEMBER 17: Former U.S. Secretary of State Hillary Rodham Clinton signs copies of her new book 'What Happened' at BookPeople on November 17, 2017 in Austin, Texas. (Photo by Rick Kern/WireImage)
Now playing
01:29
Clinton: Trump parrots what Putin says
US Democratic presidential candidate Hillary Clinton makes a concession speech after being defeated by Republican President-elect Donald Trump, as former President Bill Clinton looks on in New York on November 9, 2016. / AFP / JEWEL SAMAD        (Photo credit should read JEWEL SAMAD/AFP/Getty Images)
PHOTO: JEWEL SAMAD/AFP/Getty Images
US Democratic presidential candidate Hillary Clinton makes a concession speech after being defeated by Republican President-elect Donald Trump, as former President Bill Clinton looks on in New York on November 9, 2016. / AFP / JEWEL SAMAD (Photo credit should read JEWEL SAMAD/AFP/Getty Images)
Now playing
02:01
Clinton: What went right, wrong in 2016
ST LOUIS, MO - OCTOBER 09:  Democratic presidential nominee former Secretary of State Hillary Clinton (R) speaks as Republican presidential nominee Donald Trump looks on during the town hall debate at Washington University on October 9, 2016 in St Louis, Missouri. This is the second of three presidential debates scheduled prior to the November 8th election.  (Photo by Rick Wilking-Pool/Getty Images)
PHOTO: Pool/Getty Images
ST LOUIS, MO - OCTOBER 09: Democratic presidential nominee former Secretary of State Hillary Clinton (R) speaks as Republican presidential nominee Donald Trump looks on during the town hall debate at Washington University on October 9, 2016 in St Louis, Missouri. This is the second of three presidential debates scheduled prior to the November 8th election. (Photo by Rick Wilking-Pool/Getty Images)
Now playing
02:07
Clinton: I was thinking 'back up, you creep'
Podesta talks Trump and Clinton_00055625.jpg
Podesta talks Trump and Clinton_00055625.jpg
Now playing
07:09
Podesta: Clinton is under Trump's skin
PHOTO: Comedy Central
Now playing
01:05
Trevor Noah on the benefit of Trump's tweets
PHOTO: Drew Angerer/Chip Somodevilla/Getty Images
Now playing
02:59
Clinton and Trump aides clash
Republican presidential candidate Donald Trump speaks before introducing his newly selected vice presidential running mate Mike Pence, governor of Indiana, during an event at the Hilton Midtown Hotel, July 16, 2016 in New York City.
PHOTO: Drew Angerer/Getty Images
Republican presidential candidate Donald Trump speaks before introducing his newly selected vice presidential running mate Mike Pence, governor of Indiana, during an event at the Hilton Midtown Hotel, July 16, 2016 in New York City.
Now playing
02:52
Push back on Trump's voter fraud allegations
MANCHESTER, NH - APRIL 12: Donald Trump speaks at the Freedom Summit at The Executive Court Banquet Facility April 12, 2014 in Manchester, New Hampshire. The Freedom Summit held its inaugural event where national conservative leaders bring together grassroots activists on the eve of tax day. Photo by Darren McCollester/Getty Images)
PHOTO: Darren McCollester/Getty Images/FILE
MANCHESTER, NH - APRIL 12: Donald Trump speaks at the Freedom Summit at The Executive Court Banquet Facility April 12, 2014 in Manchester, New Hampshire. The Freedom Summit held its inaugural event where national conservative leaders bring together grassroots activists on the eve of tax day. Photo by Darren McCollester/Getty Images)
Now playing
01:38
Trump tweets slam Clinton over recount
US Democratic presidential candidate Hillary Clinton (R) and US Republican presidential candidate Donald Trump shake hands at the end of the second presidential debate at Washington University in St. Louis, Missouri, on October 9, 2016. / AFP / Robyn Beck        (Photo credit should read ROBYN BECK/AFP/Getty Images)
PHOTO: ROBYN BECK/AFP/Getty Images
US Democratic presidential candidate Hillary Clinton (R) and US Republican presidential candidate Donald Trump shake hands at the end of the second presidential debate at Washington University in St. Louis, Missouri, on October 9, 2016. / AFP / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
Now playing
06:14
Duffy: I'm with Trump - don't go after Clinton

Story highlights

Historically, October Surprises have had little effect on the outcome of presidential elections

Julian Zelizer: But this year the October Surprise could have a more dramatic effect, in part thanks to technology

Editor’s Note: Julian Zelizer is a professor of history and public affairs at Princeton University and a New America fellow. He is the author of “Jimmy Carter” and “The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society.” The opinions expressed in this commentary are his.

(CNN) —  

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.

In 1992, with just a few days left in the three-way presidential race between President George H.W. Bush, Democrat Bill Clinton and independent Ross Perot, former Secretary of Defense Caspar Weinberger was indicted for having lied to a prosecutor during the Iran-Contra investigation. The indictment brought back memories of scandals in the Reagan administration to which Bush, as Vice President, had been associated. The news certainly hurt Bush, though most agree many other factors were responsible for his defeat, including the economic recession.

An example of a small surprise came in 2000 (technically a November surprise) with the revelation that George W. Bush had been arrested for drunk driving in 1976. While the story played to the doubts that many voters had about whether he was capable of holding this job, Bush narrowly defeated Al Gore with the help of a major Supreme Court decision.

This year, though, the October Surprise could have a dramatic effect. And the most important factor is technology, which has created the most unpredictable political playing field that we have ever seen. While the concept of an October Surprise usually revolves around what one of the two campaigns might do or say in the final weeks, now we have an online world where almost any individual or organization has the capacity to disseminate embarrassing or damaging material within seconds and without any editorial barriers. With the click of a button, an anonymous person is capable of immense damage.

Adding to this uncertainty is the potential for state actors, such as the Russians, to intervene directly in the election either through the release of damaging hacked information or, even worse, tampering with US voting systems.

And the October Surprise is more likely this year than others simply because this has been a campaign where every week has revealed a new surprise. Donald Trump has already made this one of the most unpredictable races in American politics. His strategy is to constantly do what nobody thought would be done, to make statements or throw out accusations once considered out of bounds.

He also has been willing to grab onto the most tenuous claims (going back to 2012, when he was at the forefront of the ‘birther’ movement) to generate controversy and achieve attention. His recent “acknowledgment” that Obama was born in the U.S., after years of promoting this false story, combined with his move to blame Clinton for starting the birther campaign, demonstrated that he will continue to feed the interest that exists in these kinds of stories.

His strategy receives support from mainstream media, which thrives on these kinds of attention-getting moments as a way to garner ratings and fill airtime and Internet space. The convergence of a candidate who practices this kind of explosive politics with this clickbait media environment greatly increases the odds that October will look like the previous months we have just witnessed.

Then there’s the fact that the two leading candidates have intense unfavorable ratings. This means there are many organizations, politicians and individuals who don’t want to see one of these two candidates win. If the polls continue to tighten, this will greatly increase the incentives for political activists on both sides to do something that will sway the electorate their way.

Of course, in an age of terrorism, the possibilities for a dramatic event always loom large. The national security threat that Americans now face is one that is highly unpredictable since we are not dealing just with adversarial state actors or even organized terror networks but lone wolves who can cause injury, death and chaos at any time. Regardless of its origins, the bomb that exploded in New York on Saturday was a painful reminder of the kinds of fears and dangers with which we must live.

Both candidates understand there is a very real possibility they might have to adjust their campaigns if a national-security crisis were to unfold in the coming weeks.

Get our free weekly newsletter

And, finally, both candidates are extremely skilled in the art of political warfare. Clinton, because of her many decades of experience in different roles in politics, and Trump, because of his time in the media spotlight, are quite comfortable going after each other in ways that might give other politicians pause. In the final weeks, it will be time to unleash absolutely everything they have on the other.

None of this guarantees that there will be an October Surprise. Indeed, a calm final month would probably be the biggest shocker of all. But we should all hold on to our seats. For many reasons, the odds are pretty good that something shocking will happen next month.

Julian Zelizer is a professor of history and public affairs at Princeton University and a New America fellow. He is the author of “Jimmy Carter” and “The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society.” The opinions expressed in this commentary are his.”