That is just farce. Awful decision all around as it will not increase European defense, countries already have plans for creative counting how to make it on paper look like they are "spending" 5% of their GDP in defense. We could for example take Finland as example, we currently spent bit over 6 billion euros in defense, after this increase we would spent 16 billion euros in defense each year. Finland's military uses bit less than 2 billion euros to run itself (this does not include cost caused by compulsory military service, which will be left out from the increased budget). Two largest military procurements in past decade are our navy buying two corvettes with 2 billion dollars, which were ordered in 2015, and first will be delivered in 2027, so that 2 billion dollars is divided over 15 years, so about 133 millions per year. The largest purchase in past decade has been 64 F-35 with 8 billion, with 10 year delivery window, so 800 million per year. With new budget Finland can run its military and repeat both of these purchase every year and have still 2 billion to spend other things. Which is quite absurd thing to do. Only way we could actually spent that much money is to start building up massive stock of cruise missiles. But most likely we will just write all public funding for defense contractors that are selling weapons to other countries as "defense spending".
Also Trump may changes his mind about Nato next week if he feels like it.