The other NATO leaders knew any Trump threat to withdraw from NATO was silly blister, because no President can do that.
His comment that Putin could do "whatever the Hell he wants" was also, in my view, very stupid. Trump bluster is not my way of thinking at all.
And NATO countries obviously don't somehow OWE the US something because they underspent. They have their own arms producers. Germany has pretty good gear, as does France and the UK and Sweden.