Donald Trump’spresidency poses a stress test for Europe, for transatlantic relations, and for the world as a whole. Indeed, in many ways, Trump’s "America first” policy is defined by its opposition to the internationalist US foreign policy of the past eight decades.

For starters, Trump says that he trusts German Chancellor Angela Merkel and Russian President Vladimir Putin equally. Does that imply that the United States will pursue a policy of equidistance between the EU and the Kremlin?

It is not an idle question. Trump has made it obvious that established partnerships, alliances, rules, and protocols mean little to him. In his tweets, he rants about the media, attacks independent judges, targets individuals and companies, and belittles international organizations.

But even if the US under Trump is an unattractive ally for Europe, writing off the US as a European partner – which some in Europe would like to do sooner rather than later – would be a mistake.

For one thing, Europe must not ignore the majority of Americans who didn’t vote for Trump. The commitment of America’s civil society and the response of its judiciary show Europeans that the US they know and hold in high regard is no pushover. Instead of turning away from the US, we should cooperate with Americans who remain committed to preserving the transatlantic community of values. This includes members of the new administration who have voiced their clear support for the transatlantic partnership and continuity, to say nothing of Trump’s opponents – Democrats and Republicans alike – in Congress.

Moreover, those who favor cutting ties seem to believe that there are partners all over the world just lining up to defend the liberal global order together with Europe. The EU might agree with China that a new era of protectionism would be harmful. But beyond that, they have little common ground. In the long term, the liberal global order will endure only if supported by both pillars of the transatlantic partnership.

Finally, calls for Europe to become a strategic counterweight to the US are purely aspirational; in reality, no such option exists. In the short and medium term, Europeans cannot do without the US security guarantee. As a result, we must work to convince the new administration of the importance of a united and peaceful Europe.

Nonetheless, the mere speculation about decoupling European security from the US is giving rise to uncertainty, reflected in the emerging debate about a European – or even German – nuclear bomb. It’s a sham debate, because it assumes what must be questioned: Is it really in Europeans’ interest to cut the cord proactively now, before we have even been presented with any concrete US decisions that directly affect us?

Europe’s only good option is to engage with the US administration as closely as possible – which doesn’t mean playing down deeply worrying statements made by Trump. When Vice President Mike Pence, Secretary of Defense James Mattis, and a number of US senators and House members visit the Munich Security Conference this weekend, European delegates must make their expectations vis-à-vis the US administration very clear to them. Engaging and influencing is the kind of realpolitik that is necessary now, even if many Europeans may not like the idea.

This means communicating, with utmost clarity, that the breach of vital European interests would bring about a major transatlantic crisis. The worst-case scenario for Europe is a US administration that pursues policies – for example, active support for right-wing populists – aimed at bringing about the disintegration of the EU. It is equally important to ensure that any deal between Russia and the US does not come at Europe’s expense. As for the nuclear agreement with Iran, the Trump administration must be made aware that Europe will not go along with any new sanctions if the US withdraws from the deal unilaterally.

Europe can and should assert itself economically as well. If Trump really wants to introduce a kind of origin-based tax to promote US-made goods, the EU could threaten to do the same. Whether the issue is import taxes or the future of Western sanctions against Russia, it is helpful to remember the simple fact that Europe remains America’s most important market. America’s trade volume with the EU is roughly 37 times higher than that with Russia, with huge mutual direct investments locking in the transatlantic partners’ interdependence.

Even if Trump rejects such considerations, he should think twice about how far he wants to push Europe. At a certain point, anti-Trump election campaigns in Europe would probably be very successful; he will hardly be able to accomplish his plans without strong and close partners in Europe – and certainly not if he acts against Europe.

But, clearly, Europe must now focus on itself. We do need to do more to bolster our own security. While significant change is on the way, including increased integration of Europe’s armed forces, the road toward a well-functioning European defense union is long. And, in light of the precarious global situation, Germany, in particular, must increase its efforts in foreign and defense policy and development aid.

The EU’s cohesion and its internal and external security cannot be achieved at zero cost. Avoiding budget deficits, as Germany is now seeking to do, will be of no benefit to future generations if the price is the erosion of the main foundation of our prosperity: a peaceful and prosperous Europe.

Instead of waiting in fear of Trump’s next tweet, we Europeans should lay the foundations for a Europe that is strong, capable of taking action, and committed to Western values. From this position, we can assert our key interests vis-à-vis the US with confidence. That is the best response Europe can give.

Wolfgang Ischinger is a former German Ambassador to the United States.