According to Trump at the Buckinghamshire meeting with UK Prime Minister

We have 50,000 troops in Germany.

According to Answers.com, we have 68,000
According to Visual Capitalist. We have 34,805
According to Time, 37,704
According to Wikipedia, 34,821
According to Business Insider, around 35,000

So Trump rounded up to the largest group of 5 or 10 in this case. But people will say that this is him fear mongering or lying to get his way. But! But but but!
It's still a lot of troops, honestly. I mean, that's a lot more than any of the other European countries. Are we afraid of what might happen to Germany... or our we afraid OF Germany