If the people as a whole (i.e. the government) take something from one individual person, that could reasonably said to be theft. (It isn't necessarily theft, but it's not an unreasonable viewpoint.)
If the people as a whole (i.e. the government) sell something they own to one individual person, that cannot be theft. The nation cannot rob itself.
If Buffett bought the Congress, he would also need to buy the Judiciary and the Executive branches before he would have the power of a "Fuhrer".
Furthermore, the states could then revoke their consent to be governed by the Federal Government, just as they have revoked their consent to by governed by other authorities in the past (see the American Revolution, the Articles of Confederation, and the Confederate States of America).
"There are provisions for a Congressionally-declared state of martial law."
Where? I've read the entire Constitution and didn't find anything of the kind. And amending the Constitution requires the approval of 3/4 of the state legislatures.
The government represents the people as a whole.
If the people as a whole (i.e. the government) take something from one individual person, that could reasonably said to be theft. (It isn't necessarily theft, but it's not an unreasonable viewpoint.)
If the people as a whole (i.e. the government) sell something they own to one individual person, that cannot be theft. The nation cannot rob itself.
That's the distinction being drawn here.