'Accounting issue'?
You think you snap fingers and have an army, or an air force?
It's years and years of sufficient investment to create military.
I don't know why you feel it important to obfuscate what Trump called out, which was their neglect of their agreement, and their duty to be able to protect their own citizens from the threats on their doorstep, not ours.
We don't have a huge military to protect us from Canada and Mexico, we have it to protect Europe, South Korea, Japan, and Middle Eastern nations. They can damn sure carry their share of the cost.