It's pretty clear Merkel and Obama have a much better relationship than Merkel and Trump, which no doubt gets right up Trump's nose.

Trump loud caterwauling for more defence spending and less non-defence spending is repeating the same mistakes as the invasions of Iraq and Afghanistan, and more likely than not lead to even more human migration, for which Germany will pick up yet again a  hugely disproportionate share of the bill, and even more terrorism.

Trump has promised even more drone strikes. 

When the Saudis drop those munitions that he just sold them on a small village in Sadah that says " Made in America" on the side, the local tribesmen are NOT going to say "OK, no worries, We are just collateral damage. All Good!"