Trump has pushed to extricate the US from NATO, and as De Niro said in Ronin; "if there's doubt then there is no doubt".
If you want security can you really rely on someone who may or may not have your back, especially if they have a policy of transactionalism?
So, the EU needs to look to their own security, and the ultimate deterrence is nuclear weapons. And if the EU doesn't take up the mantle then the Poles will definitely do it, and probably Sweden, and possibly Finland / Germany. And so the EU needs to figure out if they are happy with a fragmented nuclear policy or not.
Russia denied there was going to be an invasion of Ukraine even the day before it started.
In 2014, nothing was going to threaten the UK's membership of the EU.
In 1989, the Berlin Wall was going to stay put for another 50-100 years.
In 1938, the UK Prime Minister waved paper promising peace in our time.
Nobody saw the Great Depression coming in January 1929.
The mesh of treaties including the Triple Entente was supposed to prevent WW1.
The southern states were convinced they had both legal right to secede and the economic support and military power that the north wouldn't try to keep them.
The British were convinced that democracy was a stupid idea and that the 13 colonies would come crawling back when they realised they needed some proper aristocrats to govern.
The world doesn't much care about things like this, pro or con.
If you want security can you really rely on someone who may or may not have your back, especially if they have a policy of transactionalism?
So, the EU needs to look to their own security, and the ultimate deterrence is nuclear weapons. And if the EU doesn't take up the mantle then the Poles will definitely do it, and probably Sweden, and possibly Finland / Germany. And so the EU needs to figure out if they are happy with a fragmented nuclear policy or not.