In one way, the US doing this makes sense. By destroying the Nordstream pipelines the US would force Germany (and others) away from dependence on Russian LNG, a turn that dependence towards the US. Great for US business, while screwing Russia at the same time.
Yes, it would be technically an act of war, but that means NOTHING today. The US fought a 20 year war without a war declaration in the Mideast (a joint resolution), a 10 year one in SE Asia (a Police Action) and a 3 year one in Korea (a Conflict)- not counting any of the other actions like Panama, the Bay of Pigs, etc... Its true for the other side as well- Russian and Chinese "advisors" seem to pop up everywhere there's a conflict too. War declarations are a thing of the past, the atomic age ended that. War is the purview of the Imperial Presidency we were warned about years ago; Congress is only consulted in case more money cant be siphoned from other areas. We'll probably only see an official "War" if it goes nuclear, and only after the fact, assuming anyone's left to declare it.