It would seem that when it comes to the transatlantic relationship and US presidents, Chancellor Merkel - who is currently campaigning for a fourth term in office - has seen it all.

She hosted the deeply unpopular George W. Bush at a wild boar barbecue in her home state on the Baltic Sea coast and the wildly popular Barack Obama for a sausage and beer breakfast in the Bavarian Alps without ever becoming really chummy with either of them.

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During the tenure of both presidents, she weathered major shocks to the transatlantic system, like the aftermath of the Iraq War and the NSA affair, but despite those strains managed to establish such solid ties with the jovial Bush and the cerebral Obama that both eventually considered her the go-to person on most matters European.

Complicated challenge

But with Donald Trump now residing in the White House, Merkel faces her biggest transatlantic challenge so far. And it comes at a time when she is under increasing pressure at home, facing a resurgent rival Social Democrats in national elections that are a mere six months away.       

"Regarding American politics it has never been as complicated as it is now," said Josef Janning, who heads the Berlin office of the European Council on Foreign Relations.

Merkel will have to take a new tack to try to establish a decent working relationship with the president, said John Harper, a US foreign policy professor at Johns Hopkins University in Bologna, since Trump is a "completely differently animal" than Obama or Bush.

That is because, unlike his predecessors - and Merkel - Trump had no previous governmental experience before becoming president.

Add to that that Trump's presidential demeanor - such as his tendency to expound quickly and aggressively on a myriad of topics, political or not, often via Twitter, or his ongoing and rather personal battle with the media - make him an outlier among recent White House occupant. He's also the polar opposite to Merkel's political style, which is routinely described as calm and collected - critics even call her bland.    

Opposing worldviews                             

While their different backgrounds and governing styles are important, these pale in comparison to the pair's vastly divergent political worldviews.

The German chancellor favors a cooperative and multilateral approach to global politics. While Trump - from what one can deduce so far - appears to favor a great power approach to international affairs, to disdain multilateral institutions and structures and to view politics essentially as a zero-sum game.

That makes finding common ground between Merkel and Trump difficult and sets the bar of what to expect from their first meeting rather low, especially given the prior verbal tiffs between them and their different domestic audiences. 

That's why neither Janning nor Harper expected any tangible results from this first get-together.  

Low expectations

"One of her interests is to get at least a good enough verbal commitment of the new president to the G20 process and to the idea of addressing issues through cooperative structures," said Janning.

Preparation for the G20 summit, which Merkel will host in Hamburg this summer, serves as the ostensible reason behind her White House visit.     

Another key topic that is bound to be broached by the pair is the future of the EU.

Trump, who has been an ardent supporter of Britain's exit from the union, has repeatedly made clear that he thinks little of the EU and prefers bilateral relationships with European countries over going via Brussels.

Given Trump's known animus towards the EU, Merkel is expected to make clear why the union is not just important for Germany and Europe, but also for the US. That could be a difficult task, noted Janning, since Trump, unlike his predecessors, has suggested that he does not view the US as responsible for European defense or as the unchallenged leader of the transatlantic alliance. Trump's stance toward Europe was on display when he received Brexit architect Nigel Farage as one of his first foreign visitors after winning the election. 

No more insults       

That's why Harper would already regard a changed tone toward Europe as success: "What I hope would come from that visit is that she can at least persuade Trump to stop attacking the European Union and to stop encouraging politicians like Marine Le Pen."

Similarly on relations with Russia, another contentious issue, Merkel will likely explain to Trump that she considers a firm stance on the shared principles and rules of the European postwar order the basis for engaging Moscow. 

Whether Merkel and Trump can find some common ground to work together will not be evident after this first meeting. But it will become more clear within the next half-year: a crucial time for Merkel, who faces re-election, and for Trump, who has to produce results.

Still, said Harper, their first meeting will likely have at least one immediate effect.

"Once Trump meets Merkel, I think it will be harder for him to insult her."