It would be very counter to the suggested goals of the US for it to demolish just 3 of the 4 pipelines. Leaving one of the brand new, larger pipelines untouched. A pipeline that had just been completed but the activation of which had been put on hold due to the start of the war. Only so that Russia could turn around after the event and offer to jointly activate this new pipeline with Germany. An act that had Germany capitulated would be a major political win for Russia, and blow to the suggested US goals.