It used to be that Republicans complained that Democrats were always trying to scare voters with the worry that the G.O.P. wanted to destroy Social Security. That may have been a valid complaint at some point but with some of the debt-reduction proposals that House Republicans have embraced, and with the leading contender for the Republican nomination calling Social Security an unconstitutional "ponzi scheme," that complaint becomes less and less valid. Here is why Social Security is not in any way a "ponzi scheme."