> how many cuts to education or defense spending save social security?

You can't save it by cutting education or defense spending. By 2036 the combined social security and medicare shortfall is projected to reach $2.7 trillion. If defense spending stays at around 3.1% of GDP--it has been decreasing as a share of GDP since the 1990s--then the shortfall in medicare and social security will be about $1 trillion more than the entire defense budget.