Use of normative MUST in politics means two things: firstly somebody concretely wants (or doesn't want for MUST NOT) which itself implies possible contentious views, opposites even, and secondly that a concrete alternative is proposed. It may be do nothing, it may be do something but the point is the alternative achieves the MUST or MUST NOT.

In this case, the proposed alternative is not do nothing. It's re-center NATO around European norms, goals and behaviours. Implicitly also a call for European NATO budgets to increase significantly, which Spain (for example) refused to do and which some European and wider partners have said MUST but.. have failed to do.

Also until recently the US government wanted that increase in spending too. Admittedly to buy US materiels but that's a detail in some ways.

He wants this. There is no imperative beyond OR ELSE.. outcomes.

NATO without the USA would be a different thing, sure, but why does the USA behaving against the interests of NATO members have to end NATO?