The US would have no problem affording that education, if it just considered taxing the richest members of its society a reasonable amount, as it did in the past.
The USA has about the most progressive taxes of all the OECD countries. In the United States high earners pay high taxes and pay a heavy share of the federal tax burden, while lower- and middle-income households pay comparatively little in direct federal income tax and there is no national consumption tax. In other OECD countries the high earners pay high taxes, but the poor and middle classes also pay high taxes including a 15%–25% national sales taxes (VAT). The US would have no problem affording that education if its tax policy was similar to all the other OECD countries, but that is not a choice voters have made.
https://www.oecd.org/content/dam/oecd/en/publications/report...
I mention both rates and "fraction of GDP" because rates can't be spent.
The maximum take is around 20%, regardless of rates, and we're there now, and have been for decades.