The controversial figure, who is still facing 91 criminal charges, now only has one rival left in the race to become the Republican candidate.
And, after he won the New Hampshire primary over South Carolina Governor Nikki Haley, most pundits are expecting another Trump v Biden race.
MI6 and the Foreign Office are even working together on a dossier about how he would impact the UK’s national security and international diplomacy, according to the i newspaper.
He told his cabinet that they need to make sure they can work together, even though Trump’s last presidency was “difficult” for US-Canadian relations.
Meanwhile, the UK and the US have long boasted of their “special” relationship – so what would it mean if Trump returned to office?
1. Could the West’s attitude to Ukraine change?
When asked by HuffPost UK about the most immediate change a second Trump term could bring for the UK, Chatham House’s director of the UK in the World programme, Olivia O’Sullivan said one “obvious concern” is Ukraine.
One of Trump’s impeachment trials centred around Ukraine, amid allegations he tried to coerce Kyiv into interfering in US politics ahead of the 2020 election.
In May last year, Trump said, if he was US president, he would settle the Ukraine war within 24 hours. He boasted he would do this by cutting off all US assistance to Ukraine, and forcing the country to make a deal with Russia.
Even if Trump just withdrew the US funding for Ukraine’s defensive efforts, it be a major blow to the beleaguered country, as the US is its largest donor.
But, this would not necessarily mean the UK and other Western countries would stop supporting Ukraine.
In fact, O’Sullivan said it could present an opportunity to “galvanise” Europe in its support for Ukraine.
That could be key as compassion fatigue is starting to hit the West, as the war is about to start its third year.
2. What might happen to Nato?
According to Politico, Trump allegedly told the EU in 2020: “By the way, Nato is dead, and we will leave, we will quit Nato.”
Even if Trump did not follow up on this promise, but did get into office, his dislike of the military alliance would most likely damage the trust each member has on each other, former US ambassador to Nato, Ivo Daalder, wrote in Politico.
Nato’s Article 5 binds all of its members together. It stipulates that an attack on one member state is an attack on the whole alliance – but would a Trump administration jump in to help if ordered to by Nato?
Only recently, Trump drew criticism from European officials after he said he “would encourage” Russia “to do whatever the hell they want” to any “delinquent” country which does not “pay” towards the alliance.
However, if the US did decide to pull out of the alliance, it would not necessarily mean it collapsed – but it would be weakened and less of an effective deterrent to geopolitical threats around the world.
But this would not just impact Nato members like the UK.
According to The Atlantic, all of the US’s security allies would question whether they could continue to count on automatic US support – and the US’s position on the world stage would falter.
3. What might happen in the Israel-Hamas war?
While the UK and the US governments have been relatively aligned over how to respond to their Middle East crisis so far, Trump’s stance on the Israel-Hamas war has been pretty unclear.
Right now, under Joe Biden, the US is Israel’s largest ally and the US president has avoided directly calling for a ceasefire in Gaza.
However, he recently told protesters he had “quietly working with the Israeli government to get them to reduce and get out of Gaza”.
Trump has not publicly encouraging Israel to limit civilian casualties (currently exceeding 27,000 in Gaza, according to Hamas-run local authorities).
Instead, he told Univision in November: “So you have a war that’s going on, and you’re probably going to have to let this play out. You’re going to have to let it play out because a lot of people are dying.”
He said Israel had to “do a better job of public relations, frankly, because the other side is beating them at the public relations front”.
The former president has also said his administration would “revoke the student visas of radical anti-American and antisemitic foreigners”, thought to be a jab at the pro-Palestinian protests which have swept across the US.
It’s worth remembering that Trump did formally recognise Jerusalem as the capital of Israel in 2017 too, and moved the US embassy there, even though the US – and most other countries – have refused to ever formally recognise it as the capital since Israel was founded in 1948.
The move was criticised for potentially increasing violence in the region, because the city is so contested between Palestinians and Israelis.
Trump has a history of hostility towards Iran, too – and the Palestinian militants Hamas is backed by the Iranian state.
O’Sullivan said: “He has well-documented antagonism towards Iran. It’s possible that he could inflame some of the worsening tensions around Israel and Iran’s proxies.”
However, she added: “I’d say the bigger thing is just that he’s unpredictable. So for the UK, that just makes it very difficult to know what to expect.”
4. Could international trade be impacted?
His remarks came after Trump hinted last year he would consider a 10% blanket trade tariffs – meaning all imports are charged the same amount regardless of how far they’ve travelled.
Hunt said “huge flourishing of global trade” has helped to tackle world poverty.
But, Trump has pushed for trade wars in the past, even claiming “trade wars are good and easy to win”.
Trump also said in February that he would introduce more China tariffs if he was re-elected – and they could be in excess of 60%.
Trump initiated a trade war with China during his previous term in office by imposing significant tariffs on Chinese goods – and Beijing retaliated.
The former president also used the economy as reasons to pull out of the pivotal Paris Climate Agreement in 2020. He claimed there was an unfair burden made on US workers, businesses and taxpayers by US pledges under the agreement.
That meant private sector companies faced less pressure to adapt eco-friendly policies, and the carbon price for other countries went up while the US’s went down.
5. Should we worry about nuclear ‘Armageddon’?
The News Agents’ co-host Jon Sopel recently compared the expected fight between Biden and Trump to “two old men fighting over a zimmer frame”.
“The only difference is this zimmer frame has a red button on it which could cause nuclear Armageddon. Should we be scared? Yeah, we should be scared that this is who could be leading the free world as we know it,” Sopel said.
But, Trump has actually expressed clear fears about the possibility of nuclear war.
He said in April last year that the world’s “biggest problem” is “nuclear warming”.
“All it takes is one madman...and it’s only a matter of seconds,” he said.
Yet, he withdrew from the Iran nuclear agreement, formally known as the Joint Comprehensive Plan of Action, in 2018.
The deal was meant to restrict Iran’s nuclear facilities but Trump claimed it did not curtail Iran’s missile programme and regional influence.
This sparked a serious response in Europe, with Germany, France and the UK saying they had “regret and concern” about the decision – and they said they were willing to continue with the deal.
6. Could the outcome from the UK general election impact how Britain responds to Trump?
It’s likely that – for the first time since 1992 – the UK and the US will hold general elections in the same year. Sunak has hinted that he will call it in the second half of 2024.
While a date has not been confirmed, according to The Sun, Sunak is thinking of calling the general election in October rather than November to avoid any global “upheaval” triggered by a potential Trump victory in the US.
Tory sources told the newspaper Sunak will aim to call the election weeks before the US’s scheduled election on November 5.
But, despite this reported caution from the Conservatives, Labour are still expected to clinch a major victory as they are leading in the polls.
Starmer hasn’t been in government before – which means a government without much experience would quickly have to adapt to Trump.
O’Sullivan suggested that, on the whole, the UK-US relationship will probably remain stable even if the former US president is re-elected.
She noted that there is a strong history of the UK and US sharing intelligence, as seen through Nato, the Five Eyes Alliance, and the recent military operations in the Red Sea.
“Many of those links did endure in the first Trump term, and they will likely endure in a second term,” she said.
“Any UK leader has to work out a way to navigate some kind of productive relationship with a US leader,” she said – even if faced with “a very unpredictable counterpart”.