I think in general the country has been skewing more "left" over the past 200 years. I see no reason why that would ever stop, programs never seem to get taken away, but new ones are added periodically. (Very quickly when you look at it over a persons life-time)
Think...
sweat shops, child labor, in the 1800s.
unions in the early 1900s
40h work week implemented
Income tax imposed
ss for only the last 2-5 years of ones life.
Now we are paying ss for 10-30 years of someones life, supporting people via various other welfare programs, ss tax has jumped many times.
If anything, I think you should plan for SS to get lowered but I think the payout will go UP in the next 50 years.