Mr Trump's stark threats during his first term in office to withdraw the US from NATO altogether, unless other member states start taking on a fairer share of the burden of European security, should have been enough to jump-start a push to rebuild European militaries - hollowed out during decades of cost-saving cuts since the end of the Cold War.
That is less than a 5% target put forward by Mr Trump, but it would at least be a step in the right direction, not just to keep the US committed to NATO, but to enable allies to rebuild their armies, navies and air forces they need to deter Russia, China, Iran and North Korea.
The eruption of the biggest conflict in Europe since the Second World War did prompt the UK and other European states to talk much tougher on the need to bolster their defences - but even then the change in the most part has been far too slow relative to the threat.
So here the UK and other European allies are all, once again, facing the wrath of an even more robust, self-interested White House, with Pete Hegseth, the new defence secretary, delivering his boss's message that Washington has bigger priorities than protecting Europe.
Repeated American administrations - not just the two Trump eras - have criticised the vast majority of NATO allies for cutting investment in their armed forces and instead reaping the benefits of a so-called peace dividend following the collapse of the Soviet Union.
