I would not be certain that Germany will follow through with sanctions. They are pushing through with the Nordstream 2 pipeline, which makes them dependent on Russia for energy. Germany is also spending well under what they promised to spend on defense and has been doing so for years.
If Russia will start actions in Ukraine, I believe that Germany will impose some kind of sanctions. But it will be just for the eyes to show that they're doing something and these sanctions won't hurt Russia much. Maybe they will froze somene's bank account or ban them from entering EU.
You have good point about weak US presidents. Same can't be said about Germany. Russia started their actions shortly after Merkel left office and new chancellor don't have that much weight in politics. I even had to Google who he is for the context.
Germany wants their Nord Stream 2 pipeline, and I recall reading that they would halt the pipeline if Russia were to invade (so brave of them, yes). It begs the question as to what actually would stop Russia if they know that NATO countries are split on what to do in the event of an invasion. The US made it clear they will not get involved, they'll just station troops in surrounding countries to watch at the dumpster fire in Ukraine.