I am a little skeptical of the US saying that Europe isn't spending enough on its military.
The UK lost hundreds of good men and women in Iraq and Afghanistan for what was an American expedition of folly, with no clear goals or plan.
It cost us billions of pounds and then ended in a matter of weeks when the US said "**** this were going home."
The US stirring up the hornets nest in the Middle East has meant that we have spent much more on the problem that manifested itself from the fallout since 2001 - Islamic Fundamentalism in the UK and Europe. The US apart from 911 has had very little in comparison to Europe to deal with.
I don't know if M15 and M16 and other counter terrorism groups budgets come from the Military but I suspect not.
The cost of this has had to be found from somewhere, with the reduction of risk from the US and China not being as much of a risk to Europe - (YET), has meant that governments have had to redistribute money from the military to home security and dealing with migrants and stupid German policies.
You could say that the US has an obligation to Europe, the US right royally fecked up the Middle East and we came to your aid, now its time for you to do the same with Ukraine.
(If Germany, Italy, Hungary, Slovakia etc aren't going to play ball, then the UK, France, Scandis and Baltic states certainly will).