No they can't. Not unless your definition of functional doesn't include the concept of actuarial soundness.
There's nothing behind Social Security except IOUs assigned to our grandkids.
Any extra tax revenues that might be envisioned via economic growth, have already been promised to banksters through the growth of the national debt.
You also must be a Marxist, if you think these socialist programs can be made to work. Maybe the monarchist Bismark did invent them as an attempt to co-opt the left, but the basic idea is a leftist transfer of wealth, and that never works in the long run.
No it just has to be changed in to a private system for the young people and pay off the old folks.