Mandatory spending has been steadily increasing as a percentage of all spending. 
Mandatory spending has been steadily increasing as a percent of GDP
While social security has been dropping as a percentage of total spending, both medicaid and medicare have been increasing -- offsetting the decrease is social security spending.
In addition, while social security spending as a percent of GDP has held remarkably steady over the last 30 or so years, the increase in medicaid and medicare spending has increased.
