The most valuable point Mearsheimer makes is that there are structural reasons why the US just won't spend as much of their manpower, resources, and efforts into defending or maintaining this close relationship with Europe, as they need to shift their focus into combating China, primarily in East Asia and Latin America.
Trump absolutely is anomalous in how openly contemptuous he is of the Europeans, but the fact is that it's no longer in the US' best interests to maintain their footprint in Europe, and any administration would begin to pivot away from the EU. It feels like only a minority of Europeans grasp that, and even fewer realize that this means their hostilities with Russia will become an albatross around their neck as they can no longer hide behind American guns.