Art 1 Sec 8 Cl 17 of the constitution grants the government authority to obtain land for the purpose of constructing military arsenals, ports, and a capital.
The federal government currently holds 640 million acres. This is 28% of the total land mass of the country.
Illegalities aside, this amount of land is expensive to own and expensive to maintain, especially for a country that is $18T in debt.
Assuming a nominal avg cost of land in the US @ $3k/acre, selling this land back to the states would net $2T to pay down on the debt. States can run the national parks as state parks or use the land as they see fit. Give the states the first option to buy, if they decline, extend the offer to private buyers. BLM manages much of this land and will no longer be needed - another $1B/yr saving



