[rsynnott]

I think to a large extent that was (and was perceived as) really just the administration saying that, rather than US expert and military leadership.

[jacquesm]

I think it was in response to Trump's statements about NATO being superfluous:

https://www.nytimes.com/2019/01/14/us/politics/nato-presiden...

That put a fire under the whole thing and made it much more clear what the various obligations would be.