When Donald Trump, president-elect of the United States, arrived in Paris on Dec 7 for the reopening of the Notre Dame cathedral, French President Emmanuel Macron greeted him with a grand welcome usually reserved for a sitting US president, with trumpets blaring and members of the French Republican Guard in full uniform.

A trilateral meeting of Trump, Macron and Ukrainian President Volodymyr Zelensky at the Elysee Palace was not on Trump's original schedule but was hastily added, making major headlines.

The scenes have been widely seen as Macron's bid to win favor from the 47th US president who will again occupy the White House on Jan 20, four years after his last term, which left a haunting memory for many Europeans.

A Dec 9 policy brief published by Bruegel, a major think tank in Brussels, stated that the return of Trump raises fundamental challenges for the European Union.

It warned that unilateral US actions could fatally weaken the three institutions critical for EU interests — NATO, the Paris climate agreement and the World Trade Organization. By threatening to raise tariffs against imports from EU and other economies, Trump's policies could have harmful effects on the EU economy.

"The EU's biggest concern is that Trump might reach a quick deal with Russia over the Ukraine crisis without even considering the EU's stance, political correctness and security concerns," said Ding Chun, director of the Center for European Studies at Fudan University in Shanghai.

Trump's election victory on Nov 5 was a huge disappointment for Europeans as a YouGov survey released on Nov 1 showed that the vast majority of Europeans wanted the Democratic candidate, US Vice-President Kamala Harris, to win. The favorability was as high as 81 percent in Denmark, 73 percent in Sweden, 71 percent in Germany and 62 percent in France, while only 6 to 15 percent in those countries preferred Trump.

However, European Commission officials expressed that the commission has been making preparations for a while for various scenarios of a Trump return.