They're going to do it again

In 1936, Kansas Governor Alf Landon, the Republican candidate for President against FDR, called the newly-enacted Social Security program "unjust", "the largest tax bill in history," "stupidly drafted," "folly," a "cruel hoax." 

Landon went on to lose the election.  He was crushed in one of the largest landslides in history.  Ever since, Social Security has been known as the "third rail" of American politics.  The reason is because the program is so popular that politicians mess with it at their peril.