Trailing in presidential polls in the final month of the campaign, President Donald Trump has seized upon recently disclosed emails allegedly from the son of Democratic candidate Joe Biden as an "October surprise" that could change the dynamics of the race.

The unverified emails were obtained by Trump's personal attorney, Rudy Giuliani, purportedly from the laptop computer of Biden's son Hunter, who was a paid board member of Burisma, a Ukrainian-owned private energy company, while his father was vice president in the Obama White House and oversaw U.S.-Ukrainian relations.

In one 2014 email allegedly from Vadym Pozharskyi, a Burisma adviser, Pozharskyi thanks Hunter Biden for arranging a meeting with the vice president. Biden's opponents point to this as "smoking gun" evidence that the Biden family benefited financially by providing Burisma access and preferential treatment from the vice president.

The former vice president has denied the allegations of corruption, has said the alleged meeting with Pozharskyi never took place and has called the Trump campaign's focus on his son's past business dealings a distraction.

"At this point in the campaign, you don't have much time left, so any arrow you have left in your quiver, however small, you're still going to try to shoot," said Mark Jones, a professor of politics and a political science fellow at the Baker Institute of Public Policy at Rice University in Houston, Texas.

History of the October surprise

The Trump campaign's effort to engineer a surprise revelation in the final weeks of the campaign to turn the election is an often-used political tactic.

In 1968, outgoing President Lyndon Johnson's announcement of a bombing cease-fire in North Vietnam on October 31 was seen by many as a move to help Democrat Hubert Humphrey's election chances. But Republican Richard Nixon easily defeated Humphrey to win the presidency.

In 1972, Nixon won a re-election landslide after his administration announced in October that "peace is at hand" in Vietnam. Nixon resigned the presidency in 1974 after he faced impeachment over the Watergate election interference scandal.

The term October surprise was coined in 1980 and referred to secret efforts by then-President Jimmy Carter to negotiate the release of American hostages in Iran prior to the election. Ultimately, the talks failed, and Ronald Reagan went on to win.

There were two October surprises in 2016 - the release of a recording of then-candidate Trump making lewd comments about women, and the FBI disclosure 11 days before the election that it had reopened its investigation of Democratic candidate Hillary Clinton's personal emails, which allegedly contained classified information. The recording initially appeared to doom Trump's campaign. Clinton was cleared of wrongdoing.

Credibility issues

The impact of this year's release of the alleged Biden emails is unclear.

Allegations that Russia played a role in perpetuating the scandal to benefit Trump could undermine the emails' credibility. Also, Trump's past impeachment for pressuring Ukraine to dig up dirt on Biden and reports that Trump paid little in taxes in the United States while earning millions in China make it difficult for his campaign to charge Biden with political malpractice.

"They have not been able to elevate the questions around Joe Biden's candidacy and potential presidency as being anywhere near dominant to the kind of controversies and chaos that really are part of this presidency," said Lara Brown, a professor of politics at George Washington University.

This year's October surprise could also turn out to be Trump's contracting the coronavirus earlier this month, refocusing attention on a deadly pandemic he has long insisted is waning.