As I've done with just about everything that makes no sense from this administration, I go back to: what would Russia want?
Russia would want the US to piss off both all of its closest allies and its largest trading partner at the same time, because it would significantly weaken the country, and potentially result in social unrest. They would want Trump to continually talk about annexing neighbors because it justifies their attempts at annexing Ukraine.
Until someone can give me an explanation that makes more sense than: Putin is pulling Trump's strings - I'm going to continue to just assume he's literally a Russian asset.