The Social Security Trust Fund should be separated out and the $2.2T IOUs paid off with new publicly traded Treasury Notes. Then the SSTF can go its own way and invest as any real pension fund would.
That would make all the national debt visible in one spot and end all the confusion about the SSTF “lock box”, “on budget vs. off budget”, etc.
The SSTF investing in world markets could reasonably expect a better return than the average 5.25% paper returns on the IOUs. At the same time, the Treasury could expect to pay less than 5.25% to those people that want/need less risk than the SSTF can afford. We’d be saving $25B/yr in interest on the national debt and the SSTF would grow $50B/yr faster than it would holding IOUs.