"the promises that are being made to those now working cannot be honored."
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A good start would be to cut military spending by 50%.

That would be a start, but leaves a lot more to do.
Here's the present Federal spending pattern as a percent of GDP:

Defense          4%
Debt interest    1
Social Security  4
Other safety net 3
Medical          4
Everything else  4
.
Total           20%

Here's where we are headed, even if we cut Defense spending in half:

Defense           2%  cut the defense budget in half
Debt interest     2   both debt and interest rates will increase
Social Security   6   the SSA estimates 6%
Other safety net  3 
Medical          10   10% estimate is for 2035, higher later
Everything else   4
.
Total            27%

In the history of our country Federal tax receipts have not been above 20% of GDP, no matter what the tax structure.

You still have a lot more to reduce. That is the source of the 'Blue Model collapse' meme (whatever you think of David Brooks).

DB2