Ok, I might have some difficulty explaining the concept, but the background for this is simple. Let's say the US SEC wants to make sure that global Bitcoin exchange prices cannot influence the Bitcoin price in their regulated market, would it not be easier for them to just allow price determination based on trading prices within exchanges that adhere to their regulations?
Let's say, they can introduce specific guidelines with rules that needs to be adhered to for exchanges to be included in their market and for price determination. If exchanges adhere to these requirements, then institutional investments can be based on your exchange trading volume, but if you do not adhere to these requirements, your exchange price will be ignored?
As for the guidelines part and forcing the exchanges to comply and monitor them this is pretty easy.
Now, the main problem in addressing this scenario is how much will the SEC really want this and how much collaboration it can get not only from other US institutions but from the rest of the world.
Case A, the lone wold tactic has close to zero chances of doing anything to global prices, or interfere with them. The SEC simply lacks the capacity of creating a virtual trade environment in the US cut from the rest of the world, it wasn't meant to do this its role is of a supervisor not a guard against the exterior, it's not designed to do this and it lacks the power that can only be granted by law.
Now, case B, when the SEC gets all the agencies to their side and backup from the Congress.
In theory, it can be achieved as the SEC would simply force exchanges that don't comply with them to cut off US citizens from trading. Then it could use their power to force every company in the US to stop dealing with exchanges that don't abide with these rules.
And at this point, it gets tricky as it's one thing to avoid US citizens from using your platform is something totally different to try to avoid US banks and their subsidiaries that are all over the world. Basically, some will be simply cut off from the flow of money and the ones that can cash on the US funds will have a better position, look at it like some sort of state aid.
After this, they can simply start to pick up the foreign exchanges that don't obey their rules one by one, and we all know the US doesn't give a crap if it's NZ, Greece, Romania or Thailand when it comes to arresting people and putting them on a plane before anyone has a clue what's happening.
So yeah, in theory, if the SEC goes full berserk it could achieve some sort of control over the markets.
Of course, there would be still a black market, but if they do manage to get some allies on board the black market would be so small it would not be able to influence the price anymore.
But this scenario is totally improbable, it requires tons of paperwork, of laws, of cooperation between government agencies and at this point, they simply don't give a damn about the prices. 100 billion? 200 billion? Those are peanuts right now.