Early voting has revolutionized how Americans select presidents and lawmakers, turning Election Day into a full season and marking the “October surprise” for extinction.

More than 78 million Americans cast a ballot before Election Day, including record turnout in swing states such as Georgia and hurricane-battered North Carolina.

Most Americans this cycle reported they would cast a ballot before Tuesday, an increase from pre-pandemic levels. It is a sea change that is forcing candidates to define their opponents and campaign pitches by late September.

When Vice President Kamala Harris challenged former President Donald Trump to a second debate in October, the ex-president said there was no point because people were already voting.

The comment reflected the Republican Party’s acceptance of early voting after criticism of the pre-Election Day voting cost the party dearly in 2020. It appears to be paying dividends in swing-state Nevada, where the Republican held a five-point lead over Democrats in mail and early in-person voting totals.

The parties are seeing mixed results elsewhere. A surge of female voters in Pennsylvania is causing angst among Trump supporters, though an uptick in new male Republican voters in Arizona provides a counterweight.

“Republicans have made massive voter registration gains, and we are far outperforming in our share of the early vote relative to two or four years ago across all battleground states,” said Trump campaign national press secretary Karoline Leavitt.

Ms. Harris tried to counteract the Republican Party’s catch-up act by advertising on the illuminated Sphere in Las Vegas and timing rallies in Pennsylvania, Wisconsin and other swing states with the beginning and end of early voting.

“It is so, so easy to join your friends and cast your ballot. I’ve already voted. I sent in my mail-in ballot about a month ago,” Mason Garrigan, a senior at the University of Wisconsin, Stevens Point, said during a Wisconsin rally Monday with Ms. Harris’ running mate, Minnesota Gov. Tim Walz.

Voters can submit ballots before Election Day in various ways, including absentee ballots or in-person voting, known as “advance voting.”

Advance voting began to proliferate around the 1970s but can be traced back a century to a 1921 Louisiana constitutional provision that said, “the Legislature may provide a method by which absentee voting will be permitted other than by mail,” according to The Associated Press.

Broader options do not mean faster results. Mail-in and absentee ballots, which voters are using at historic levels, will slow down tallying on Tuesday and will likely delay the presidential election results in some battleground states.

Voting rules vary by state. According to Vote.org, a nonpartisan nonprofit, early voting is prohibited in Alabama, Mississippi and New Hampshire. In Illinois, Minnesota and Vermont, generous periods start 40 or more days before Election Day.

Pennsylvania, a critical swing state, has a system known as “in-person mail ballot voting” that allows a person to request a ballot and submit it in person.

Voting before Election Day is often limited to a select number of locations rather than the full array of polling sites. Its main appeal is the ability to avoid long lines and vote when someone pleases, especially if they have a long work shift or other duties on Election Day.

With voters having their say several weeks in advance of Election Day, there is less sting from a so-called October surprise in which damning information harms or helps a candidate.

A warm-up comedian for Mr. Trump on Oct. 27 called Puerto Rico a floating pile of garbage and President Biden responded in kind by calling Trump supporters garbage, causing an uproar. Yet by then, tens of millions of people had voted.

A Gallup poll released on Halloween found a majority — 54% — of registered voters planned to cast a ballot before Election Day.

While that is down 10 percentage points from 2020, when the pandemic fueled early mail-in votes, only 40% voted early in 2016, 35% in 2012, 32% in 2008 and 21% in 2004.

Voters in each party had similar early voting rates until 2020, when Democrats were far more likely to cast votes before Election Day.

Mr. Trump cast doubt on mail-in and early voting during that campaign, saying elections should be a one-day affair. Suspicions around early voting and potential voting appeared to backfire on the Republican Party, which lost the White House race and squandered the Senate by losing seats in Georgia in January 2021.

What a difference four years makes.

“ABSENTEE VOTING, EARLY VOTING, AND ELECTION DAY VOTING ARE ALL GOOD OPTIONS,” Mr. Trump wrote on Truth Social in April.

Voters of all kinds are heeding the call, and some states are smashing records.

More than 4 million people in Georgia voted before Election Day, causing Republican elections officials to boast after critics said a 2021 election overhaul law would lead to voter suppression and people withering from thirst in polling lines.

“For those that claimed Georgia election laws were Jim Crow 2.0 and those that say democracy is dying … the voters of Georgia would like to have a word,” Gabe Sterling, the chief operating officer for the state secretary of state, said on X.

North Carolina, a battleground with 16 electoral votes, said more than 4.2 million people took advantage of early in-person voting, smashing the previous record of 3.6 million despite fears that devastation from Hurricane Helene would suppress totals.

When absentee votes are included, nearly 4.5 million people — 57% of the state’s registered voters — cast ballots before Election Day.

“Candidates and their campaigns now have to consider its ‘Election Month’ and not just ‘Election Day’ in this state,” said Michael Bitzer, director of the Center for North Carolina Politics & Public Service at Catawba College. “They must have a well-organized ground game operation and their GOTV efforts have to be constantly updated to reflect who has cast a ballot already, thereby avoiding wasting time and resources on banked ballots from voters.”

It’s hard to tell who has the edge from early voting. Mr. Bitzer pointed to an “unprecedented” three-way tie in party affiliation of voters: 32.4% Democrats, 33.6% unaffiliated and 33.3% Republican.

Mr. Trump’s son, Donald Trump Jr., told early voters at a Raleigh rally on Monday to use their free time wisely on Tuesday.

“It means you have all day tomorrow to bring your friends to the polls,” he said. “Do not take anything for granted.”

• Tom Howell Jr. can be reached at thowell@washingtontimes.com.