It is debatable if everyone but John Bolton and Donald Trump knows this. After all, according to the last NYT poll the current POTUS commands an approval rating of 41 % in the USA. The number of people I meet who do not understand how tariffs work, for example, is staggering.
Anyway, it is smart policy to expect the worst and plan for it instead of being surprised by another insane president voted in by the people of the USA. Call it risk management if you like. It would be negligent of the leaders of the EU and its member nations to not account for that. The EU has to reduce dependence on unrealiable trade partners, this is true whether we are talking about warmongering Russia, dictatorial China (probably the most reliable of the three!), or unpredictable USA.
So, let's hope for the best and prepare for the worst. The EU can't change it if preparation harms US economic interests in the long run. That's on Trump.