I would suggest that sixty to seventy percent of Germans have simply moved on, and generally accepted the fact that Trump is the US President. A quarter of the German population has some driven purpose in Trump-denial, and five-percent probably still think that Obama is President (don't laugh, it's pretty much a fact with some of German society).
So when engaged, to explain how this all happened....I suggest the five 'triggers' or explanations on this.
1. While unbelievable to most....it is not a highest-vote type of election. It is a fifty-state election, and states are weighted in their electoral college votes to ensure each has a contribution to the election. It's NOT rocket science....it's routinely discussed in university courses, and throughout high school. You can attract all the votes you desire in urbanized zones like Atlanta, Memphis, Boston, Philly, Miami, etc.....but if you can't get a 270 vote via the fifty-state mechanism, then you won't win. You need a campaign which speaks to states, NOT to the individual.
2. Ever since the NAFTA Agreement of 1994, three US Presidents have come and gone....promising Americans jobs....which slowly drifted out to Mexico and China. The only real growth of jobs that you can establish is the burger-industry and government jobs. That's it. Hillary Clinton and Donald Trump both discussed jobs. Most people put Clinton into the category of the previous three presidents and had marginal faith in something happening. With Trump, there was belief that he might be able to reverse the trend and actually deliver jobs. If he delivers one-million new jobs into the market over the four years, then it will have been considered a success. If not, then the public will move on.
3. The middle-finger syndrome. Like it or not....a large number of the American public are fed up with the news media. They don't have any real trust in what is said or speculated about. So for these Americans.....Trump serves as a middle-finger. They want the news media to falter, stumble, and in cases collapse. As many times as German public TV journalists quote the NY Times or Washington Post....they've tended to have lost traction with the American public. Same story for CNN.
4. The two Americas. There's urbanized America, which leans mostly toward Democratic candidates and rural American which leans mostly toward Republican candidates. It has not always been this way, but in the past thirty years....more so. Seventy-percent of counties in America (3,000 of them) leaned more toward Trump, than Clinton. Suggesting that the rural America is not intellectual enough to grasp the situation....tends to get you noticed....that you aren't capable of grasping the change of the landscape or the priorities of the general public. Using the intellectual argument....just makes you look foolish in the end.
5. Loss of faith in the system. DC to most Americans has become some collection of 'empty-suit' actors, corrupted politicians, and lobbyists with various agendas. You can ask either working-class Republicans or Democrats....it doesn't matter, their faith has been shaken. They want something to change.
Like or not.....the system was built to deliver the prime selection of fifty states. It did what it was designed to do. If Trump wasn't qualified for the job, fine....but the system wasn't built to determine qualifications. If it had been.....you might not have seen either Clinton or Trump as President.