On the left, we have US Government social spending vs total US Government receipts. If the two lines were to meet, it would mean that it takes all the money collected by the Federal Government to only cover social spending. On the right, social spending is broken down by program, and displayed as a % of GDP. Notice how Medicare+Medicaid has blown past Social Security back in the mid 1990s, and continues to do nothing but rise. Unemployment spending rises during recessions and falls during recoveries.
Next, social security broken down by % of population, and the cost of each group receiving benefits as % of GDP. Social security has 3 groups; retirees, survivor benefits paid to the spouse and dependents of retirees that have died, and disabled workers. You can see that retirees are the major driver of costs.