With passions at fever-pitch, many Americans believe the November 3 election is make or break for the US, regardless of whether they back Donald Trump or Joe Biden.
But whether the Republican business tycoon remains in the White House or if his Democratic challenger ousts him will also have a profound effect on the rest of the world, including the UK.
The “special relationship” with the US is more important than ever after Brexit, but it is by no means the only major issue at play when America votes.
– Personal relations
Boris Johnson has a firm relationship with the president, with a certain amount of mutual admiration between the pair. Mr Trump has regularly lavished the Prime Minister with praise and has referred to him as a “great guy”.
But there can be no doubt that Mr Trump is a tough man to deal with on the world stage and the departure of his mercurial attitude to foreign policy would be welcomed by some.
Lord Darroch, a former British ambassador to the US, has predicted the pair’s bond could grow even closer if Mr Trump wins a second term, saying: “Boris can be his best friend in Europe.”
With Mr Biden, on the other hand, the Prime Minister may have less of a natural ally and the UK will need to rapidly court him with fears he could favour closer ties with other European powers.
The Democratic challenger last year described Mr Johnson, fairly or not, as “kind of a physical and emotional clone of the president”, who he openly despises.
Mr Biden has already expressed concern at the Government’s controversial Brexit legislation with the UK Internal Market Bill (UKIMB).
– A trans-Atlantic trade deal
Mr Biden treasures his Irish heritage and has warned that a UK-US trade deal is “contingent” on respect for the Good Friday Agreement that brought peace to the island and the prevention of a return to a hard border.
His warning came in response to four US congressmen warning Mr Johnson of their “grave concern” over the UKIMB, which could see the Government break international law in overriding the Northern Ireland Protocol agreed with Brussels in the Withdrawal Agreement.
There is speculation that Mr Biden could favour Berlin over London, particularly owing to Barack Obama’s closeness with German chancellor Angela Merkel during Mr Biden’s tenure as his vice-president.
Mr Trump, however, is a long-standing supporter of the UK’s departure from the bloc and has even referred to himself as “Mr Brexit”.
He has spoken of brokering a “phenomenal trade deal”, which Mr Johnson craves in order to demonstrate a benefit of leaving the bloc.
But Mr Trump is a notoriously tough negotiator and many have warned of a race to the bottom for UK food standards and greater privatisation within the NHS from a deal with the tycoon.
– The climate emergency
With the UK hosting the United Nations’ COP 26 climate conference next year, a victory for Mr Biden could alleviate a headache when it comes to the environmental crisis.
Mr Trump, who has called climate change a “hoax”, is pulling the US out of the Paris climate agreement to keep global heating to “well below 2 degrees Celsius above pre-industrial levels”.
His opponent, however, has vowed to immediately rejoin the accord, a move that would be welcomed by Downing Street.
A second term could further embolden Mr Trump in his “America first” strategy in distancing the nation from international allies.
His former national security adviser, John Bolton, has suggested Mr Trump could wrench the US out of the Nato military alliance with Europe, which he believes relies too greatly on American spending.
Mr Biden, on the other hand, believes Nato is critical to collective security and has accused his opponent of an “abdication” of responsibility over his threats.
– The Iran nuclear deal
Mr Trump pulled the US out of the Joint Comprehensive Plan of Action, which was brokered by Mr Obama at a time when western governments believed Tehran was close to making a nuclear weapon.
The UK, France and Germany, along with Russia and China, remain signatories to the accord, but it is on life support after alleged breaches by Iran.
Mr Biden said he would revive US participation in the deal if Tehran “returns to strict compliance”.