Florence Gaub nailed it at Raisina:
'... the United States could not sustain a two-front war [against Russia and China] ... Europeans have a critical security vulnerability that's going to get worse over time if we're not acting now ... We're not doing this for Donald Trump. We're doing this because we have to do it ... perhaps that's the blessing in disguise of President Trump, is that he forces European publics to accept that this [mil-spending] is no longer something you can have but it's something that you have to have ... not spending enough on defense to be able to actually sustain [NATO] Article V obligations, that's also undermining it [Article V]. So, I think without wanting to defend the White House, I think, in general, transatlantic commitment relies on both words and tools'.
https://youtu.be/KyhijmN5hks