I think he'll actually pull through with this.
At least considerably reduce US military presence in Europe and have its NATO members shoulder more financial responsibility for their own defense.
Which they won't be able to do, thus weakening and exposing Europe to Russia, which now sees the EU/NATO as an existantial threat and strategic enemy it'll have to deal with decisively eventually.
European nations will have to choose between keeping up their social and retirement systems or expanding their militaries to fill the vacuum left by the US withdrawal. Which will lead to mass impoverishment, economic distress and widespread societal destabilization of the EU, while still being unable to create an effective defensive military infrastructure.

Which will lead to WW3 by Russia invading a weak and ailing Europe with its modernized army before the end of this decade, as long as it still has the necessary demographics for it.

So it has been foreseen.