The decision to cancel election night celebrations may also reflect the unusually politicized nature of the American diplomatic corps. Most of the State Department's top envoys around the world are political appointees and allies or donors of the sitting president. The current US ambassadors in major European capitals, for example – such as Ambassador Mark Gitenstein in Brussels and Ambassador Jane Hartley in London – are close allies of Democratic President Joe Biden.

A spokesman for the U.S. Embassy in London said it “appreciates the longstanding energy and excitement surrounding the U.S. presidential election, conducted over nearly 250 years of democracy,” but added that “Election Day does not end with Election Night.” It may take some time until the votes are counted and the electoral process can take place.”

The comments highlighted another reason why diplomats may be avoiding public scrutiny on election night: There is deep unease about the strength of the U.S. democratic system after disputes over the outcome of the 2020 election led to an attack by Trump- led supporters to the US Capitol.

Eight years after 2016, the cautious approach to election night also reflects the very different approach Europe is taking this time around the prospect of a Trump presidency. After being caught flat-footed by Trump's victory in 2016, European and American leaders are determined not to allow the same thing to happen again.

The EU, like governments across Europe, is planning for a possible Trump victory after being completely blindsided in 2016. Last month, Björn Seibert, a top official to European Commission President Ursula von der Leyen, teamed up with ambassadors from 27 countries and other top officials to model how the bloc will respond to the US election.

Although transatlantic relations will face challenges, the possibility of a second Trump presidency has the EU worried whoever wins on November 5 – Vice President Kamala Harris has signaled she will prioritize American workers and raise tariffs. Trump's political vision could have a devastating impact on EU-US relations: his plans to increase tariffs would likely trigger a trade war, while he has called on Europe to commit more to defense and Ukraine and has refused has to commit to NATO. Not to mention what a Trump presidency would mean for international climate cooperation, which could pressure Europe to step up its own efforts to address the climate crisis.

One person who will have some champagne on ice is strongman Hungarian Prime Minister Viktor Orbán, who called Trump last week to wish him luck. In fact, Orbán, whose country holds the six-month rotating presidency of the EU Council, will invite European leaders to a summit in Budapest later this week once the US results are available. He has said he will open “several bottles of champagne” if Trump wins – but he might drink alone.

Sarah Wheaton, Rosa Prince and Clea Caulcutt contributed to this report.