I don’t know the truth of the matter and Seymour could be right. We just can’t tell from the evidence provided.
This pipeline had been completed but activation was stopped due to the start of the war. If Germany had capitulated and activated it with Russia that would be a major political win for Russia and blow for the suggested goals of the US and other allies. To me this seems to be the biggest hole in the theory that the US was responsible.
(2): Then why blow the other three?
So for the US angle to work here what is the motivation?
At the outset of the war Germany stopped NS2 activation plans and started diversifying its energy away from Russia.
Leading up to the explosion Russia had been trying to blackmail Germany by reducing the supplies of gas. And gas was fully turned off at the time of the explosion. Russia was also playing games with Germany to try to get propaganda wins over the subject of gas by cutting gas supplies on NS1 and saying it was because Germany needed to ship it a turbine. Then Russia was claiming it couldn't receive the turbine from Germany because of the sanctions imposed by other countries. Russia was also saying, well pity that we can't supply enough gas because we don't have the turbine, but we could activate NS2 with you instead. [1]
So the clear motivation for the US could be that they did not want Germany to capitulate to Russian blackmail and give Russia some kind of political or sanction relief. That's actually somewhat reasonable as a theory if you believe Germany was susceptible to it (was it?), and assume all the other levers that the US and other EU allies had wouldn't be enough to keep Germany on the team.
The risk is that doing this and being caught would be a huge breach of trust. The claim of Hersh is that these explosives sat on the pipeline for three months.
The US even warned Germany about potential attacks on the pipeline. [2]
So now if that is the motivation, in this context leaving one of the newer, larger NordStream 2 pipelines untouched would make absolutely no sense. As you leave open the possibility for Germany to still capitulate and worse give Russia a massive propaganda win by forcing Germany to reverse its position and activate NS2.
[1] https://www.nytimes.com/2022/08/03/business/germany-russia-g... [2] https://www.reuters.com/world/cia-warned-berlin-about-possib...