It depends upon the demographic patterns -- if we restored a 1950 population pyramid:
it would in fact solve it completely. If we push retirement ages up and keep either making or attracting lots of young people to enter the workforce, SS and Medicare are sustainable.
But focusing entirely on spending is masking the bigger issue. Medical costs are going to show up
somewhere in the economy -- either in the government account or in personal accounts. Moving health costs to the government side of the ledger is not, in and of itself, a bad thing, as long as it realizes efficiencies (this is what the debate should be about) and, if we do it, that they are paid for in revenues (also what the debate should be about, but never will be with one side claiming that all taxation is theft blah blah blah).
The main problem we have is not that we have grown government, it's that we have grown government and
refused to pay for it. Some costs are certainly best left with individuals, some definitely should be pooled like insurance under government accounts. The rule for how we divide those costs should be utilitarian. I don't particularly think there are big Constitutional concerns, but say there were -- that's why the Constitution is amendable.
This is not intractable. It just requires honesty. The main problem is not politicians lying to the electorate; it's the electorate lying to themselves.