Joe Biden v Donald Trump - four things that could decide who wins

Donald Trump and Joe Biden will do battle in November to determine who occupies the White House for the next four years.

This contest will be unique in modern history as a rematch between the current president and his immediate predecessor.

The contrast will be simple, according to Sean Spicer, who served as Mr Trump's first press secretary and worked for the Republican National Committee prior to that.

"For those people who say, well, during Trump, the policies of Donald Trump made my life better, more secure, made the economy and our communities better, it's a no brainer."

The Trump campaign will be hoping to distract from the weaknesses of their candidate - his legal troubles, his divisive rhetoric and his attempts to undermine the 2020 election results, which contributed to the January 2021 attack on the US Capitol.

But Mr Biden also has key vulnerabilities, struggling to sell his first-term achievements and trying to convince the public he has the energy for the campaign and a second term.

He paints his predecessor as out-of-control and a threat to America, and to democracy itself.

"Here, you've got somebody who's very well known, and you're just trying to prove he's a big risk." says Susan Estrich, a Democratic author and analyst who managed Michael Dukakis' presidential campaign in 1988.

It's a rematch few Americans say they want but it's a presidential choice that at this point they seem almost certain to get.

Here are four factors that will determine who comes out on top.

Mr Biden's approval ratings continue to languish in dangerous territory for an incumbent entering an election year. Public perceptions of Mr Trump are also negative, however.

By all indications, November's general election is going to be tight. National polls show the two candidates either neck and neck or Mr Trump with a slight advantage.

But this early in the race they are of limited usefulness, given the nature of the US political map. While Americans will head to the polls across the nation, this race will once again be decided in only a handful of states.

That's because the electoral college, the system the US has to pick its president, depends on candidates winning each state and most states are solidly Democratic or Republican.

The most crucial states that could go either way this year include Wisconsin, Pennsylvania and Michigan in the so-called Rust Belt, and Arizona and Georgia, two states that Mr Biden flipped Democratic in 2020.

Nevada is also considered a toss-up but its small population makes it a less valuable prize.

A few states that have been battlegrounds in previous election cycles have slipped off this map - Florida and North Carolina have trended Republican of late, while Virginia and Colorado appear to be more solidly Democratic.

So while national polls provide fodder for political commentators, a much smaller subset of voters will ultimately be the ones who matter.

Polling showing Mr Trump inching ahead in these key states have caused alarm among some Democrats, but the size of his lead is not statistically significant.

When it comes down to it, Americans tend to vote from their wallets in national elections - for the governing party in good times and the opposition in bad.

"It's the economy, stupid" was the mantra of Bill Clinton's successful 1992 presidential campaign, and the refrain has become political gospel in the decades since.

One of the factors that makes 2024 challenging to predict is that, on the whole, economic indicators are positive.

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The economy is growing at a steady clip. Unemployment is near record lows. The stock market is hitting record highs. And yet American voters continue to have a grim view of their economic situation.

Some of this can be attributed to several years of high inflation and the continuing high cost of housing in many parts of the US. Home sales in the US have sunk to the lowest levels in nearly 30 years.

At the Trump victory party in Iowa, two large video screens cycled through graphics showing how rising home mortgage interest rates during the Biden administration have driven up monthly home payments.

There are some recent signs of hope for Mr Biden, however.

In March consumer confidence, as measured by a University of Michigan survey, reached its highest level since July 2021. Inflation and gas prices have fallen well below their recent highs. There is still plenty of time for voters to change their minds about the state of the American economy.

Mr Trump will argue that things were better when he was in office.

According to Mr Spicer, the economy - like crime - is a "gut" issue and many Americans still don't believe their everyday situation has improved.

"Until you viscerally feel it," he says, "it doesn't matter what statistic gets thrown at you."

Mr Biden will counter that the US weathered the post-Covid economic storm better than almost any other country in the world and that Bidenomics - his blend of infrastructure investment, tax cuts and social spending - has improved the lot of working Americans.

The Biden campaign will try to convince voters that Mr Trump is responsible for abortion becoming illegal or greatly curtailed in dozens of states, even as the former president has tried to moderate his position on the issue.

Ever since the US Supreme Court, with the help of three Trump-appointed justices, discarded a 50-year precedent giving the right to abortion constitutional protections, Democrats have been riding a groundswell of support on the issue to post better-than-expected results at the ballot box.

Mr Biden has pointed to state court decisions approving stringent new abortion restrictions in Florida and Arizona, along with upcoming voter referendums on the subject, to encourage liberal voters head to the polls in November. Vice-President Kamala Harris has held rallies across the country focusing on women's reproductive rights.

"Abortion has turned out to be a much more powerful issue than a lot of people thought it would be," Ms Estrich says. "Everywhere it's been on the ballot, the pro-choice position has won."

If abortion is the electoral issue the Democrats will be trying to elevate in the minds of voters, Mr Trump and the conservatives will be doing the same for immigration.

Border crossings reached an all-time high in December with 249,785 arrests on the Mexican border - up 31% from November and up 13% from December 2022, the previous record. They have been falling in recent months.

This massive influx of undocumented migrants and asylum-seekers has at times overwhelmed government processing facilities and strained social service programmes in major cities thousands of miles away.

Polls show that immigration is the top issue for much of Mr Trump's base - and a source of weakness for the president and division among Democrats.

Efforts to address the problem in Congress have proven unsuccessful, in no small part because Mr Trump has been pressuring Republicans to block compromise legislation until after the election.

"The Biden administration has lost the argument on safety and security at our southern border," says Mr Spicer. "It's over."

Other issues might also play a factor in the upcoming presidential race, including US crime rates, the environment and climate change, and foreign policy.

The Gaza War, in particular, might be an ongoing headache for Mr Biden, as the administration's support for Israel has angered some Democrats, including a larger percentage of the young voters whose turnout in November could decide the election.

The longest general election campaign in recent memory leaves plenty of time for the unpredictable to occur.

Given the advanced age of both Mr Biden (81) and Mr Trump (77), an incident that calls into question their health and fitness could happen any time.

In the autumn presidential debates, their energy and composure under pressure will be particularly scrutinised.

"Age is hurting Biden right now. Everybody thinks Biden is old," say Ms Estrich. "The question is, will Trump show the signs of his age?"

Given that polls indicate a majority of Americans are dissatisfied with their two major-party options, the environment is ripe for a third-party or independent candidate to emerge.

Robert Kennedy Jr, the anti-vaccine activist, is polling in double-digits nationally, although he is only on a handful of ballots so far. Left-wing academic Cornel West is also running, and the Libertarian and Green parties will field their own candidates.

Mr Trump's legal headaches could also factor into the race - he faces 91 charges and four criminal trials. Although the indictments seem to have buoyed his standing among Republicans, a criminal conviction may be a different matter.

According to an exit poll of voters in the New Hampshire Republican primary, 42% said Mr Trump would not be fit for office if he were found guilty. Polls of voters in other Republican primaries have produced similar results.

Although several of Mr Trump's highest-profile trials have been repeatedly delayed, the spectacle of Mr Trump in the defendant's dock and a detailed litigation of his alleged crimes could affect public opinion in a way that the indictments have not.

The January 2021 attack on the US Capitol by his supporters, with Mr Trump accused of egging them on, has left a scar on the American psyche.

While Republican voters appear willing to move past it, Democrats - and, perhaps, the kind of independent voters who will help decide this election - still remember.

The more they are reminded of that trauma, and the way the first Trump presidency ended - whether by Mr Biden and the Democrats or through courtroom drama - the more the former president's past actions may ultimately come back to haunt him.