5 things we don't know heading into 2024 election

Polls show that the 2024 general election is shaping up to be a rematch between President Joe Biden and former President Donald Trump.

Beyond that, much remains unclear.

Both candidates ran unconventional campaigns in 2020 during the height of the coronavirus pandemic. Both helped rejigger their parties' bases and who typically turns out to vote. And this time, speculation is running rampant over how third-party and independent candidates will impact the electoral calculus in November.

Here are five uncertainties heading into the new year.

How does Biden campaign?

Biden largely ran his 2020 campaign from his home in Delaware amid skyrocketing concerns over COVID-19, which states severely struggled to contain at the time.

Republicans knocked him for running his campaign from "his basement," but the strategy ultimately paid off -- helping him adhere to public health guidance at the time, avoid publicized gaffes and emerge for events just before the general election to inject his base with a dose of 11th-hour enthusiasm.

That strategy likely won't be run back this time around.

But Biden now has the benefit of living in the White House, which past presidents have used as the world's most famous political backdrop in their own reelection bids.

It remains unclear what kind of balance Biden plans on striking between blitzing the campaign trail and staying at the White House -- but that balance is likely to draw extra scrutiny amid speculation over Biden's age. At 81, he is the oldest U.S. president to be in office.

An active campaign schedule could help the president rebut allegations that he's not fit for another term, while a Rose Garden campaign could attract even more attacks from Republicans that he's lost a step.

"2024 will be all about scaling up our operation and taking the President's message of democracy, freedom, and building an economy that works for every American directly to the voters that will decide this election," Biden campaign spokesperson Seth Schuster said in a statement. "In the first months of 2024, we will continue to scale up our campaign infrastructure so that by the early summer -- when we expect voters to be thinking about the election more -- our campaign is operating at full steam."

How does Trump campaign?

Trump was far more active than Biden during the 2020 election.

While he also canceled many events during the pandemic, he returned to the campaign trail much earlier than his opponent, sparking controversies over whether he was prioritizing his political ambitions over the public's health.

This time, he won't have a pandemic to grapple with, but he could be limited by a calendar packed with trial dates in the four cases he's currently fighting.

While polls shows that Trump is the overwhelming favorite to win the GOP nomination, his trials are already playing a role in his primary strategy, with Susie Wiles, a top campaign advisor, telling reporters that the campaign wants to "front load [events] as much as we can" because the calendar of potential court dates is "a scheduling nightmare."

"The goal is to take him off the trail at a very critical time and it's our job to make it less of a critical time," she said, referencing hopes for Trump to all but lock up the nomination before heavy primary days such as Super Tuesday.

Steven Cheung, a campaign spokesperson, also told ABC News that Trump "will outwork everyone on the trail."

Who might not vote?

A major mystery that may not be solved until the days leading up to, or even after, Election Day is what kinds of voters choose to go to the polls and who chooses to stay home.

The two party bases have become jumbled over recent cycles, largely falling along lines of education and wealth.

Biden was ushered to victory with large backing from a coalition of college-educated white voters, Black voters and Hispanic voters. Trump, meanwhile, got a large swath of his support from white voters without a college degree while making gains with male voters of color.

Who among those coalitions turns out next year could be the election's deciding factor, polls suggest.

A recent New York Times/Sienna College poll showed Biden trailing by 2 points among registered voters -- but up by 2 points among likely voters. More specifically, Biden has a 6-point lead over Trump with voters who voted in 2020, while Trump boasts a 22-point lead among those who didn't vote in 2020.

That trend of Democrats' support among high-propensity voters is supported by a spree of wins for the party in off-year elections, which typically see lower turnout.

There are several variables at play as to what will push voters out to vote, including reactions to the overturning of Roe v. Wade, frustrations over the economy and personal opinions on Biden and Trump, each of whom are prominent boogeymen for the opposing parties.

Will candidates running with third parties or as independents make the ballot?

The rumor mill is in full force over how independent and third-party candidates will impact a hypothetical but likely Trump-Biden rematch.

But first they have to get on the ballot -- and doing so is easier said than done.

Jill Stein, who is running on the Green Party line, will be able to appear on many ballots, benefiting from her party's existing ballot infrastructure.

But candidates such as Robert F. Kennedy, Jr., and Cornel West are running independent of any organized party. No Labels, the group that is pushing for a "unity ticket" on its own ballot line, also is on its own.

They will have to garner enough signatures in each state to appear on the ballot, with different states having different thresholds that need to be reached.

Hitting the requirements in all 50 states will likely be difficult for the candidates and groups starting from scratch. West himself forecasted to POLITICO recently that he anticipated making the ballots in 40 states instead of all 50.

No Labels is still only on the ballot in 12 states: Alaska, Arizona, Arkansas, Colorado, Florida, Hawaii, Mississippi, Nevada, North Carolina, Oregon, South Dakota and Utah.

Will there be a defining issue?

A Trump-Biden rematch represents a unique set of circumstances, pitting against each other two candidates with universal name recognition and solidified brands.

Frustration over the elimination of federal abortion protections has spurred Democrats to wins in the 2022 midterms and off-year races in 2023. And polls show voters have a dour view on the economy -- and mostly blame Biden for their woes.

Yet given widespread and, strategists say, cemented opinions of the two likely nominees, character is set to play an outsized role next year, particularly regarding Trump's brash rhetoric, legal exposure and role in the Jan. 6, 2021, insurrection and Biden's age and fitness for office.

"I believe that the fundamentals of a Biden-Trump race are locked in," one GOP strategist who is supportive of Trump and asked not to be quoted by name to discuss the race, told ABC News earlier this month.