RFK Jr. says he'll have the U.S. buy $615B of Bitcoin if elected president.
Not sure he can but I do believe he is sincere with the thought. 
Discussion
Spending power is with Congress but a President can just veto budgets until he gets what he wants. The political uproar would be insane though. Imagine the caterwalling about welfare checks not going out or Army soldiers not getting paid because a President wants Bitcoin.
There hasn't been a budget in decades.
there's a budget every year.
There isn't. Not the way there used to be. We have a dent ceiling crosos and then aassove spending bill rushed through without any debate or itemized vote.
Those aren't budgets.
Forgive the typos... I've got fat thumbs...