20 reasons global debt time bomb explodes soon, page-2

I am worried about this
"America's debt at 84% of GDP will soon pass that toxic 90% trigger point."

does anyone know anything about this 90% trigger point?
please explain

things that may help it get to that level are
defense
medicare
pensions
the bailout is already factored in

the us needs to reduce spending on defense and put the money into pensions and medicare

i see two problems
1. the risk of the government going broke

2. shadow banking
3. something in china eg a bursting of the property bubble
4. another terrorist attack

3 of these are black swans - low probability, big impact

gov going broke
shadow banking
a terrorist attack

the most likely will be a bursting of the property bubble in china.