The point is, if not for NATO, then Germany would be perfectly within its rights to say "with all due respect, Mr Trump, fuck off".

But since Germany are a NATO member state, and since gas is a critical resource, Trump is right in saying that Germany is under Russian influence. And that is a problem for NATO. What's the point of NATO if member states are going to support the enemy's economy while being energy dependant on them? That kind of relationship means political influence.

Germany should be seeking an alternative source, even if it costs more.