Out of the embers of World War II, the United States has largely been there for Europe.
With NATO, it provided security, amidst the threat posed by the Soviet Union.
With the Marshall Fund, an organisation dedicated towards US-European cooperation, recovery was comparatively smooth.
And with political support, the US helped lay the foundations for the EU itself.
But four years of the Trump presidency has challenged those transatlantic norms, with trade wars, a questioning of the military alliance and a view that the EU is a threat rather than an ally.
Euronews spoke to three key experts on how a win either way could affect the bloc.
Would a President Biden restore that more familiar relationship?
"He will try and repair and restitch the multilateral alliance, particularly with the EU which is one that we know he has a long history with," said President Barack Obama's former advisor, Robert Malley.
"Now, that doesn’t mean it is going to be that easy to go back to square one, there has been a lot of damage done, not just in eroding trust, but I think Europe will know that when you have President Trump one day and President Biden the next, who knows who will come after that, so Europe will probably feel the need to deepen its strategic anonymity if that is the right word, even if relations with the US improve, I suspect quite dramatically in the wake of a victory by Joe Biden."
There are concerns in some quarters about a second Trump term. How do you see that affecting the future of the EU?
"The biggest fear is that the EU would fall apart because you would have one camp who would see the Trump two Presidency as an opportunity to double down on European sovereignty and you would see another camp that would try to stick with the United States whatever it takes and that can easily divide the European Union. That is the biggest fear here in Berlin, we are always the ones that want to hold the club together and work with the Poles and the French, and north and south," Jana Puglierin, Senior Policy Fellow at the European Council on Foreign Relations explained.
America has been moving its focus in a direction away from Europe for decades, pivoting east to Asia and China. Is this rebalancing likely to continue?
"There are structural reasons why the rise of China makes a difference to the United States but also the general focus to Asia. We are after all a bi-oceanic country, a bi-oceanic power, that has always been part of our makeup. You could see a rebalancing for sure. There are also demographic changes in the United States, generational changes that probably push in that direction as well, clearly, younger people in the United States are paying more attention to Asia, probably a bit less to Europe. But there are still overwhelming reasons for the United States to care about this relationship with Europe," Ian Lesser, Vice President at the German Marshall Fund told Euronews.
Four years of Donald J. Trump have proven to be a cold, hard slap in the face for much of Europe, but it is a reality that has been coming for a long time and maybe an opportunity too, for the EU to define and assert its own united foreign policy position more.