Not sure we need 5%. Maybe countries that have short-shrifted defense should spend 5% until they made up their arrears. And maybe we should commit to as big a number as will scare the bejesus out of Putin. 5% and no war is way cheaper than a war with a nuclear-capable adversary.
Anyway:
Russia: 6% of $2 T.
US: 3.5% of $30 T.
NATO (not including US): 1.5% of $22 T.
Obviously, Spain (1.2%) and also Canada, Portugal and Italy (1.5%) have to step up to the bar.
Trump is, right now, looking at sanctions on Spain.
Also, we (US) have obligations all around the world (ex., stopping Iran from getting nukes). The Europeans have to accept primary responsibility for Europe.