For the person in the street, there's really very little support for defense spending, and polling indicates this is true of both self-identified Republicans and Democrats - the only thing preventing huge cuts are local pork issues, really. And the average person is completely unconcerned about the Chinese, Russian militaries, etc.
Regardless of whether that's the correct view, that's the simple reality out there right now.
As you chart shows the real battle has already begun, i.e., Guns versus butter. Throughout history, this is a common thread as great powers in decline must make these decisions. Butter usually wins because it has the most constituents. Europe is a prime example of what happens. Most European countries plus Canada spend 1% or less of their GDP on defense.
As the welfare state demands more and more resources to keep it afloat, taxes are increased and defense reduced to make up the short falls along with increased borrowing. The US is well along that path as the welfare state collapse. Our population of those over 65 will double in the next 20 years and by 2030, one out of every 5 residents of this country will be 65 or older. And by 2030, there will just be two workers for every retiree compared to 3.3 today and 16 in 1980.
Only suicidal idiots plan their defense on past conflicts. Laugh your ass off all you want, but the fact is that our nation is in decline which is led by our waning military. Tell that to your grandma.