U.S. election day is around the corner, and the presidential candidates, Donald Trump and Kamala Harris, are in what promises to be a nail-biting race to the finish.

The outcome of the election is critical to America’s future and that of the rest of the world—perhaps nowhere more so than Europe.

The old continent has come to rely heavily on the U.S. for trade and defense guarantees, which raises the stakes for the region as it grapples with economic volatility, slipping competitiveness, the rise of right-wing nationalism, and heightened security risks due to Russia’s invasion of Ukraine.

Take Trump, for instance. He has made no secret of his ambitions to make European trade more expensive, adding to stock market jitters that the region could emerge a loser. And Harris could put further pressure on Europe to push away from China.

Fortune spoke to leading experts ahead of the election to share their analysis of the potential impact on Europe.

1. Crippling tariffs

The U.S. is the European Union’s largest trade partner. Over time, the countries have established a mammoth-sized trade relationship that employs 16 million people on both sides of the Atlantic and trillions of dollars in trade and investments. That’s not all—half of Europe’s output comes from trade, which now stands exposed.

Trump, the Republican candidate, plans to impose an additional 10%-20% in cross-border tariffs, making trade expensive and possibly weakening the euro.

“Tariffs will seriously dampen the EU’s economic growth,” Zach Meyers, assistant director of the Centre for European Reform, told Fortune.

This isn’t a far-fetched outcome, given Trump slapped tariffs on steel and aluminum imports from the region during his first term as president. More tariffs could hurt economies like Germany’s, which has been struggling and is heavily dependent on U.S. exports, shrinking GDP by 0.23%, studies show.

“The prospect for retaliatory measures regarding the $350bn+ of US exports to Europe means households and businesses would be faced with higher prices, which would eat into consumer spending power and hurt corporate profits in Europe,” said James Knightley, ING’s chief international economist.

Brussels is already gearing up for how the election and a harsh tariff regime could play out.

However, if Europe wins an exemption from Trump’s tariff regime, it “could boost European firms’ relative competitiveness in the U.S.,” said Meyers.

Tariffs are Trump’s modus operandi. On the other hand, Harris would take a more diplomatic approach and increase pressure on the EU to reevaluate its economic ties with Beijing. After all, the U.S. has used its diplomatic clout to nudge Europe before—including cutting ties with Chinese telecom giant Huawei.

Either way, Meyers expects that the three-way relationship between the U.S., China, and Europe will likely get complicated. Harris would encourage European companies to make more goods in the U.S., carrying forward the approach of her predecessor, President Joe Biden.

Both Trump and Harris will likely hike tariffs on China, forcing the Asian superpower to dump more exports on Europe (than it currently does) and increasing the risk of a full-blown trade war, Meyers said.

2. Business uncertainty

While tariffs are one way to put “America first,” as Trump touts, the election could just be the beginning of an overall global shift in mood music.

“There is concern that President Trump could bring significant change to both the economic and geopolitical environment,” said Knightley. “Harris is effectively the continuity candidate and as such is viewed as less threatening.”

Europe’s trailing competitiveness in tech, innovation, and defense has become an “existential challenge,” as former European Central Bank President Mario Draghi highlighted in September.

“There are growing worries that the EU also needs a stronger role in AI to avoid a new set of future dependencies,” Meyers said. In a recent report he coauthored, Meyers suggests that aligning U.S. and EU tech regulations might benefit both countries by improving productivity and the trade of tech services.

While Europe is trying to boost its standing in the fast-paced and cut-throat world of innovation, it’s also built a notorious reputation for scrutinizing U.S. Big Tech companies for their online safety and antitrust practices.

Trump recently complained about the EU imposing a multibillion-dollar fine on Apple, promising to take action if he wins the election. He has hit back at European regulations in the past, too.

There is much uncertainty—and curiosity—about what each candidate could mean for Europe’s ability to innovate and regulate. However, the region is still largely responsible for changing its fate on that subject.

“It is really up to European policymakers to create an environment that can allow them to grow and scale up to the level to compete with the major U.S. names. Unfortunately, I am not confident that will happen,” Knightley said.

3. Defense

Geopolitics is another key area where the two candidates’ differing approaches could impact Europe. Years of poor defense investment and the escalating Russia-Ukraine war have left the EU in a position where it needs the U.S. for support.

In that backdrop, “the Trump effect on Europe and the EU will be negative—more negative than it would be in the Harris administration,” Steven Blockmans, an associate senior research fellow at the Centre for European Policy Studies, told Fortune.

Trump has threatened to quit NATO in the past. He even went so far as to say that he would “encourage” Russia to “do whatever the hell they want” to NATO countries that don’t pay towards the alliance, Politico reported earlier this year. If Trump decides to change course on supporting Ukraine, European countries will increase defense spending quickly to bolster national security.

Harris has said that if elected, she will stand by the defense alliance and Ukraine. She is expected to largely follow Biden’s foreign relations path with a few tweaks of her own.

Blockmans said the big question regarding a second Trump administration is whether “it will still be adults in the room” when making policy decisions.

Another risk of a Trump 2.0 is that his power could embolden other far-right European leaders, such as Hungary’s Viktor Orbán.

“There are very strong streaks of autocracy in Trump’s approach,” Blockmans said, cautioning that other factors also influence the popularity of Europe’s political figureheads beyond the influence from across the Atlantic.

“In 2024-25, Europe and the EU’s [are] unfortunately in a more dependent situation in transatlantic relations, and that is why it matters even more that there is stability, predictability, and support.”