YES they can.
They were made by Law and cab be removed by Law. That is why they want control of the US Supreme Court and many other legal forums and agencies of the USA.
Just recently, under pressure by Grumpy Trumpy (who only camps in his Mar Lago Golf Course or the bunker) a huge park in Alaska (Alaska’s southern Brooks Range.) was given a 'special' permit for road development prior to mining, all for millions at the govt expense!
Wait! This was a declared FEDERAL WILDERNESS - this is the opposite of what the law says since this is a 100% protected area. NO NEW DEVELOPMENT IS ALLOWED.
Yes they can sell the US National Parks - because their buddies want that land and resources. It's that simple for them. That's what they paid for...when they supported and elected Trump.
They can be smart - sometimes. They will throw smoke bombs all over the place - abortion rights, law and order, maybe make a few 'new' parks...But in the end the parks can be SOLD or restrictions removed. Little by little they can do it.
I worked to save the Gray Whale Park in Santa Cruz CA. We succeeded - it became a park - next to UCSC. But the key is that I helped organize massive support from UCSD students. They played many games - calling and suspending hearings etc.
You need that - MASSIVE ORGANIZED support from all of us: happy campers! We must give back our love to these parks!
Maybe all OUR great times in those parks will become just memories, and our children never know what it was like an immense OPEN spaces....SAD, VERY SAD.
-- Raul, Yunque explorer