Remember how the big deal with Nixon was, "he went to China." The background for that historic visit was twenty years of Republican gnashing about "who lost China," following Mao's seizing power, which laid the political groundwork in the United States for our Vietnam War. That is, the most liberal President we had since FDR was unable to resist the flow of events towards all out war in Vietnam primarily because he was afraid of "losing" Vietnam. This was the "domino theory," and the basis for much of our Cold War foreign policy. Nixon could turn this domestic context on it's head because Nixon possessed (at the time) unassailable right wing cred, including his pursuit of the continuing Vietnam War. He could finally break the silence between the U.S. and China.
The same situation more or less pertains with regard to Social Security. Democrats, in this case, have maintained a defense of Social Security against all Republican attacks, and Republicans have gotten no where with their various schemes to undermine the system and the safety net it provides to many millions of Americans at the lower end of the financial ladder. Following the "he went to China" principle, then, it would follow that a Democrat would have the most chance of actually changing Social Security in a significant way. In this context, consider the following analysis and discussion.