HAMBURG — Few things are as scary to European governments as the prospect of another Donald Trump victory in 2020. In less than three years, he has already taken a wrecking ball to transatlantic relations. If he has another five years to play with, the relationship could be reduced to little more than rubble.

The U.S. president has insulted allied leaders at every turn even as he’s fawned over authoritarians from Moscow to Pyongyang. His understanding of NATO appears to be rudimentary at best. When it comes to the European Union, the Trump administration is often outright hostile; America’s envoy to the EU reportedly went as far as saying that it was his job to destroy it. Whether it’s over Iran or climate change, finding common ground is getting tougher and tougher. In most European capitals, Trump is so unpopular that a policy will instantly become less attractive if he backs it.

The silver lining, so the popular narrative goes, has always been that Trump’s presidency will make Europe more united.

Faced with the bitter truth that America is set to remain an unreliable ally for years to come, some say Europeans will have no choice but to push ahead with the European project. EU governments will find ways to cooperate more closely on foreign and security policy and, thanks to heavy investments in military capability, become less dependent on the United States. The result would be a more united Europe that speaks with one voice and takes care of itself, taking on the role of steadfast defender of the liberal international order.

This is all entirely possible — but unlikely.

European leaders like to give grand speeches about the need to save the liberal international order, but they are reluctant to expend blood or treasure in its defense.

Historically, American support has played an integral role in bringing Europe together. Diplomatic support aside, U.S. security guarantees provided the conditions necessary for the emergence of the European Union in the first place. As the American security umbrella becomes less trustworthy under Trump, old fault lines will become more visible and new divisions will emerge.

As NATO weakens, some European countries will attempt to strike bilateral deals with the U.S. to guarantee their security. Others will argue in favor of pushing full steam ahead for some sort of European solution. At the same time, the EU will be losing one of its most powerful militaries to Brexit.

It’s also unclear how united a front Europeans will be able to put up as defenders of the liberal order. European leaders like to give grand speeches about the need to save the liberal international order, but they are reluctant to expend blood or treasure in its defense.

French President Emmanuel Macron wants Europe to move closer to Vladimir Putin’s Russia; German Chancellor Angela Merkel is unwilling to ban Chinese companies from sensitive network infrastructure in Germany for fear of upsetting the Chinese Communist Party. If this is what’s happening now, imagine what Europeans would be willing to do after another few years of Trump.

Europe is still in denial about how bad things could get. It’s increasingly popular among European politicians to call for the EU to get rid of the need for unanimity on foreign and security policy decisions. The difficulty of finding consensus, they argue, is holding Europe back. But far from a necessary answer to Trump’s America First approach, this risks only making things worse.

We cannot expect powerful nations to use their resources to implement foreign policies that they reject. Scrapping the need for unanimity might work in other areas, but it’s a recipe for disaster in foreign and security policy at a time when Euroskepticism is already rampant. Instead of making it easier for the EU to act as one entity, it would be a gift to populists from left to right.

Europe can only move forward at the speed of its most skeptical members. And that will become increasingly difficult if the White House exploits differences between the EU’s member countries. (And there’s no reason to think it will be shy about doing so: See Trump’s support for a no-deal Brexit.)

Europe can’t wait around in the hope things will go back to the way that they were.

Merkel was right when she said that Europe has to do more to take its fate into its own hands.

That doesn't mean Europe can afford to turn away from America completely. It will need to walk a difficult tightrope and pursue policies that achieve both objectives at the same time: build up its self-reliance and maintain good relations with Washington.

If there is to be any hope of NATO’s survival in the long term, Europeans will have to contribute more.

An obvious place to start is to invest heavily in defense. The U.S. has long pressed Europeans to contribute more to their own security and that policy will not change, even after Trump leaves office.

If there is to be any hope of NATO’s survival in the long term, Europeans will have to contribute more. And if the U.S. becomes yet more unreliable, or NATO ceases to provide meaningful deterrence, Europeans will definitely have do much, much more. They might as well get started now.

Marcel Dirsus is a political scientist based in Hamburg and a non-resident fellow at the Institute for Security Policy at Kiel University (ISPK).