• "Whoever wins will be 'America first'," a senior European diplomat, who did not want to be named due to the sensitive nature of the transatlantic relationship, told CNBC.
• Trade with the United States is extremely important for European nations.
• The EU and the U.S. have the largest bilateral trade and investment relationship in the world, which reached an all-time high of 1.2 trillion euros ($1.29 trillion) in 2021.

European politicians and policymakers are busy preparing for more American protectionism regardless of who emerges as the next leader of the White House after elections next week.

The presidential race has remained a dead heat going into its final few days, with polling consistently rating the candidates, Vice President Kamala Harris and former President Donald Trump, as being tied within key battleground states and across the country.

"Whoever wins will be 'America first'," a senior European diplomat, who did not want to be named due to the sensitive nature of the transatlantic relationship, told CNBC last week.

"The main concern for the Americans is the economy, and the answer will have to be more economic nationalism — I don't agree with it, but I don't see any way around that," said the senior diplomat, who takes part in confidential talks among the EU leaders.

The comments come after a warning from German Finance Minister Christian Lindner, who on Friday told CNBC there could be retaliation if the U.S. kicked off a trade war with the European Union.

"In that case, we need diplomatic efforts to convince whoever enters the White House that it's not in the best interest of the U.S. to have a trade conflict with [the] European Union," he said at the IMF annual meetings in Washington, D.C.

Trade with the United States is extremely important for European nations. The EU and the U.S. have the largest bilateral trade and investment relationship in the world, which reached an all-time high of 1.2 trillion euros ($1.29 trillion) in 2021, according to data from the European Commission, the executive arm of the EU.

Harris is seen, to some extent, as likely to continue current President Joe Biden's policies, which in economic terms will be remembered in Europe by the Inflation Reduction Act — a sweeping U.S. legislation totaling $369 billion which targets climate and energy policies. The IRA upset many European leaders due to its perceived protectionist nature.

The "America first" policy is likely to have more repercussions for European economies under a Republican presidency. Trump has threatened to impose additional across-the-board tariffs of 10% on European products, which could put a strain on the bloc's exporters and, according to data from Goldman Sachs, weaken the euro by as much as 10%.

Trump's first tenure at the White House was a challenging time for some European leaders, who expressed their dislike for the former president's style and confrontational tone. The two sides often had differing views on trade, defense and technology — among others.

"Trump cannot surprise us anymore, we know how to handle it, we have had to deal with him before," the anonymous senior diplomat also told CNBC.

A second EU official, who also requested not to be named due to the sensitive nature of the U.S. relationship, told CNBC: "There's no panic. We are being very pragmatic, but of course we have to prepare for both scenarios."

The same official added that the European Commission is working on "bold" initiatives regardless of who becomes the next president.

CNBC reported in May 2023 how European officials were already quietly preparing for the possibility of a return of Trump. This meant a focus on cutting dependencies with the U.S. and with China — something that EU leaders continue to target.

In an October statement, the 27 heads of state of the EU called for "more efforts to enhance the Union's competitiveness, strengthen its economic resilience, secure its industrial renewal and achieve the full potential of the Single Market."

"It highlights the urgency of taking effective action," the statement added.

Champagne to celebrate?

Beyond the European institutions in Brussels, there is some division across the various EU capitals with regards to the U.S. presidency. National leaders have made differing remarks about the potential for a second Trump presidency.

Hungary's Prime Minister Viktor Orban reportedly told journalists in Brussels this month that he would open "several bottles of Champagne" if Trump returns to the White House. Just two days after U.S. voters head to the polls, EU leaders are expected to meet in the Hungarian capital of Budapest and will likely discuss the outcome of the election over dinner.

A third EU official, who did not want to be named and who will be attending the meetings in Budapest, told CNBC: "I am definitely not going to celebrate if Trump wins." The same official added that the U.S. election is "very worrying" as it "comes down to 200 votes in [swing state] Pennsylvania."

The official added that, whatever the result, "it won't come as a shock as it did last time, and Europe has since improved its strategic autonomy and defense spending."