What are the 2 most expensive entitlement programs?

Can you tell me what are the two most costly entitlement programs that are currently being implemented? Are these programs sustainable in the long-term given the current economic climate and potential fiscal constraints? What measures are being taken to ensure their financial stability and to prevent any potential future overspending? Additionally, how do these programs compare to other forms of social welfare spending, and what are the arguments for and against their continued funding?