As chances increase of a Joe Biden-Donald Trump rematch in the US presidential election, America's allies are bracing for a bumpy ride.
Many worry that a second term for Mr Trump would be an earthquake, but tremors already abound – and concerns are rising that the US could grow less dependable regardless of who wins.
With a divided electorate and gridlock in Congress, the next US president could easily become consumed by challenges at home, before even starting to address flashpoints around the world, from Ukraine to the Middle East.
French President Emmanuel Macron's recent verdict was blunt: America's “first priority is itself".
The first Trump administration tested the bonds between the US and its allies, particularly in Europe.
Mr Trump derided the leaders of some friendly nations, including Germany’s Angela Merkel and Britain’s Theresa May, while praising authoritarians such as Turkish President Recep Tayyip Erdogan and Russian leader Vladimir Putin.
He has called China’s Xi Jinping “brilliant” and Hungary’s Viktor Orban “a great leader.”
In campaign speeches, Mr Trump remains sceptical of organisations such as Nato, often lamenting the billions the US spends on the military alliance whose support has been critical to Ukraine's fight against Russia's invasion.
He said at a rally on Saturday that, as president, he would warned Nato allies that he would encourage Russia “to do whatever the hell they want” to countries that did not pay their way in the alliance.
Mr Trump also wrote on his social media network that in future the US should end all foreign aid donations and replace them with loans.
Nato Secretary General Jens Stoltenberg warned that Mr Trump could be endangering US troops and their allies.
“Any suggestion that allies will not defend each other undermines all of our security, including that of the US, and puts American and European soldiers at increased risk,” Mr Stoltenberg said in a statement on Sunday.
Mr Biden, meanwhile, has made support for Ukraine a key priority and moral imperative.
But his assertion after his election in 2020 that “America is back” on the global stage has not been entirely borne out.
Congressional Republicans have stalled more military aid for Ukraine, while US influence has been unable to contain conflict in the Middle East.
Thomas Gift, director of the Centre on US Politics at University College London, said that whoever wins the presidential race, the direction will be the same – towards a multipolar planet in which the US is no longer “the indisputable world superpower".
Most allied leaders refrain from commenting directly on the US election, saying it is for Americans to pick their leader.
They are conscious that they will have to work with the eventual winner, and behind the scenes, governments will be doing the “backroom work” of quietly establishing links with the contenders’ political teams, said Richard Dalton, a former senior British diplomat.
But many of America's European Nato allies are worried that with or without Mr Trump, the US is becoming less reliable.
Some have started to talk openly about the need for members to increase military spending, and to plan for an alliance without the US.
German Chancellor Olaf Scholz said he was “currently on the phone a lot with my colleagues and asking them to do more” to support Ukraine.
Germany is the second-largest donor of military aid to Kyiv, behind the US, but Mr Scholz recently told German weekly Die Zeit that the country could not fill any gap on its own if “the US ceased to be a supporter".
Mr Trump's comments on Saturday about Nato rang alarm bells in Poland, which shares a border with Ukraine.
“We have a hot war at our border,” Polish Prime Minister Donald Tusk said on Sunday.
“We must realise that the EU cannot be an economic and civilisational giant and a dwarf when it comes to defence, because the world has changed.”
Russia, meanwhile, is busy bolstering ties with China, Iran and North Korea, and trying to erode Ukraine’s international support.
Mr Macron also said American attention was focused far from Europe. If Washington's top priority is the US, he said its second is China.
“This is also why I want a stronger Europe that knows how to protect itself and isn’t dependent on others,” he said in January.
Mr Trump has supporters in Europe, notably pro-Russian populists such as Mr Orban.
But former British prime minister Boris Johnson raised eyebrows when he recently said “a Trump presidency could be just what the world needs".
Mr Johnson is a strong supporter of Ukraine in its struggle against Russian invasion, whereas Mr Trump has frequently praised Mr Putin.
Mr Johnson said in a Daily Mail column that he did not believe Mr Trump would “ditch the Ukrainians", but instead help Ukraine win the war, leaving the West stronger “and the world more stable".
Bronwen Maddox, director of UK-based think tank Chatham House, said such arguments underestimate “how destabilising” Mr Trump has been, and would probably continue to be if elected.
“For those who say his first term did not do much damage to international order, one answer is that he took the US out of the JCPOA, the deal to curb Iran's nuclear programme," Ms Maddox said recently.
"Iran's acceleration of its work since then has left it a threshold nuclear weapon state."
Mr Biden was a critic of Mr Trump's Iran policy but has not managed to rebuild bridges with Tehran, which continues to threaten across the region.
Mr Dalton, a former UK ambassador to Iran, said prospects for the Middle East would be “slightly worse” under Mr Trump than Mr Biden.
But he said divergence on the region’s main tensions – the Palestinian-Israeli conflict and Iran's ambitions – would be limited.
“No US administration is going to make a serious effort to resolve differences with Iran through diplomacy,” Mr Dalton told AP. “That ship sailed quite some time ago.”
Palestinians and their supporters implore Mr Biden to temper US support for Israel as the civilian death toll from the war in Gaza climbs.
But hardliners in Israel say the US is already restraining the offensive against Hamas too much.
Itamar Ben-Gvir, Israel's far-right National Security Minister, recently said Mr Biden was not giving Israel his “full backing” and that “if Trump was in power, the US conduct would be completely different".
Mr Trump developed a strong rapport with Turkey’s Mr Erdogan, calling them “very good friends” during a 2019 meeting at the White House.
Yet Turkey-US relations were fraught during his tenure. The Trump administration removed Turkey from its F-35 fighter jet project over Ankara’s decision to buy Russian-made missile defence systems.
Mr Trump threatened to ruin Turkey’s economy.
Russian Foreign Minister Sergey Lavrov said in January that he does not “believe there will be any difference” between a Trump and a Biden presidency.
He said Russia-US relations have been going downhill since George W Bush's administration.
With China, where leaders’ initial warmth towards Mr Trump soured into retaliatory tariffs and rising tensions, little changed under Mr Biden, who continued the tough stance towards the US's strategic rival.
Zhao Minghao, a professor of international relations at Fudan University in Shanghai, said that for China, the two candidates were like “two bowls of poison".