Errr... they did 'end it' back in February 22. In case you didn't read the news Germany cancelled its cooperation on the project back then. No need to blow it up, just stop work on it and don't use it to transport gas, end of story and it hasn't been touched since. And again it would be glaringly obvious to all NATO members if work ever started up again or gas started flowing through it! So again NATO including the US had no need to destroy it. Nord 2's tap was turned off. Nord 1 was active but Germany was paying for its gas. Funnily enough though sabotaging NORD 1 does 'punish' Germany as the main customer. Now who do you suppose would want to do that in a way that has plausible deniability while sending a message that the same thing could happen to other critical undersea NATO country infrastructure?