I don’t know an answer at this point in time that would be politically viable.
Given the current state of the market, one could privatize, social security, medicare and medicaid by allowing people under a certain age to invest most of their contributions in private investment accounts and means test the benifits for people older than that age. Unfortunately, most people are totally incapable of putting a dollar in their own pocket without it burning a hole in their pocket and older people would never accept a reduction in their “benefits”.
My only other suggestion would be to cut the federal budget in half and eliminate all unnecessary programs. So much of the Federal Budget is wasted on unnecessary and unconstitutional programs.
There’s a lot of fat to cut in absolute terms but in relative terms it doesn’t matter. In 2018 the federal budget was $4.1 trillion. $2.5 trillion was social security, Medicare/Medicaid, and unemployment. Of the rest, 650 billion was on defense contracting and the other $650 was every other gov’ts program (nasa at $20bn, state department at $44bn every other federal agency, farm subsidies at $10-$20bn, etc etc).
Getting rid of everything but defense spending wouldn’t even dent the growth in entitlement spending, only cutting benefits will fix the issue.