Calling for lowering the mobilization age in Ukraine down to 18 now also called by Trump team...
Why?
This is a message not only to Ukraine: "You lost the war" - knowing that this measure would tear down the Regime in Kiev - but also to people in USA and Europe - "if there is a war - you all have to go..."  
He also has sent a message to war criminals in Tel Aviv by posting a very critical video from Jeffrey Sachs - "get your shit together or else..."
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And by threatening to take Greenland Trump sends another message to Europe:
Do what we want (in Ukraine) or get fucked.
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It is all messaging.