The antifa in Hamburg also put the First Lady [Donald Trump's wife] in danger.
https://www.thesun.co.uk/news/396824...-g20-protests/
This should be reason enough for the US to declare Germany a failed state, invade the country, disarm the military and police, round up the antifa, and then establish a new government that will maintain law and order and curtail any future antifa.
The German government is apparently either unable or unwilling to maintain order and protect its decent citizens from violence at the hands of revolutionary cut-throats and thugs, similar to what is going on in Venezuela, the state is smiling and nodding as non-state actors engage in violence against regime enemies with the tacit approval of the regime.
Germany's government is illegitimate and should be overthrown by a coalition of reasonable powers, powers such as Russia and the USA. The USA could insert US Army Special Forces [Green Berets] into Germany and begin arming and training native Germans to rise up.
Germany is a threat to NATO and a threat to the collective security of Europe because they are betraying NATO and allowing millions of future jihadi fifth columnists into the heartland of Europe, similar to what France is doing.
Were I the President of the USA and my wife were pinned down in a hotel in Hamburg because German police were refusing to do anything to control an uprising of antifa in the city, I would have gotten on the phone with European Command of the US military and ordered that a brigade from southern Germany be dispatched to Hamburg without delay, and that the 173rd Airborne Brigade Combat Team be deployed out of Italy into Hamburg and that they use any and all necessary or prudent force to get into Hamburg and secure the area around the hotel.
I would probably tell Merkel "you'll do what you're best at, nothing, or else you'll be in a prison cell awaiting trial before the end of the month."