The two have substantive differences in their politics as well, and they’re not just over immigration and asylum policies. Trump’s worldview, organized around the unfettered pursuit of America’s narrowly defined national interest, leaves little space for policy cooperation or compromise. Yet these qualities are at heart of what Merkel values and practices given Germany’s central role in the European Union (EU).

The security of the Western world hinges on whether these two leaders can find common ground. Sooner or later, trans-Atlantic relations will face a test: a terror attack, war, or some other crisis. America and its European allies will have to make important, irreversible decisions in real time. Responding to such a test is impossible without a degree of trust and reliable communication, which we can only hope the Trump-Merkel tête à tête will help establish.

In two areas in particular, Merkel and Trump ought to be on the same page—or if not, at least reading from the same book.

The first is security. Trump’s beef with Europeans in general and Germans in particular is that those countries are, in his view, shirking their responsibilities toward NATO and the general trans-Atlantic defense alliance.

That is a fair criticism. Germany currently spends 1.2% of its GDP on defense. The problem is not that Germany’s leaders or public are flaky when it comes to spending more on security. Rather, their aversion to playing a more assertive security role reflects the country’s historic experience. For nearly a century prior to the creation of NATO, German militarism plunged the continent into catastrophic conflicts.

That said, there is a case for Germans to do more—and in fact, they already are, investing more into conventional capabilities, drones, and cybersecurity. In order to prevent the catastrophes of the past from happening again, Germany ought to boost its military spending in concert with other European nations. It can do so through platforms such as NATO and the European Defence Agency.

On that note, Merkel has to make a compelling case to Trump that preserving and supporting the European project is squarely in America’s interest, notwithstanding what the president might hear on cable news or from his chief strategist Steve Bannon. Especially if Trump’s ambition is to strengthen NATO by pushing Europeans to be more engaged, he ought to remember that a divided continent of economically disjointed nation-states will not make for a very good alliance.

Unlike Trump, Merkel has interacted with Russian President Vladimir Putin for over a decade and understands the Kremlin’s threat better than any world leader. She also remembers what Soviet domination meant for Central and Eastern Europe. Hopefully she can steer Trump away from repeating the mistake of his two predecessors, who believed that resets and accommodation would make Putin’s Russia a constructive partner.

The second, and no less important, task is for Merkel to nudge Trump away from his protectionist instincts. The opening of markets and liberalizing reforms across the world have been responsible for the greatest reduction of poverty in human history. At the same time, global free trade has little to do with the productivity, wage stagnation, and disappearance of manufacturing jobs in developed economies. Trying to cure those problems by reversing globalization, as Trump suggested during his campaign, would have disastrous consequences for the world.

It would be a pity if the Transatlantic Trade and Investment Partnership (TTIP), a proposed free trade deal between the U.S. and EU, were abandoned after three and a half years of negotiating efforts. It would be even worse if the Trump administration decided to pick a trade fight with Germany, one of the largest foreign investors in the U.S.

To be sure, there is truth in Peter Navarro’s criticism of the macroeconomic imbalances exacerbated by the common European currency, the euro. That, however, is the eurozone’s problem to fix. The common currency is by no means a lever for Germans to deliberately “undervalue” their currency in order to boost their exports. Merkel should try to reassure Trump on this point, and encourage him to reconsider his opposition to the TTIP.

Most importantly, Merkel’s visit is a learning opportunity for the new U.S. president. The German chancellor—who might not be in office beyond September with Germany’s upcoming elections—has seen successes, failures, and compromises, and engaged in occasional overreach and almost constant firefighting. It is sometimes said (most recently by British historians Charlie Laderman and Brendan Simms) that American presidents have little opportunity to learn on the job, relying instead on the intellectual capital they’ve accumulated in prior experiences. If Trump approaches his meeting with Merkel the right way, he might become an exception to the rule.

Dalibor Rohac is a research fellow at the American Enterprise Institute.