My understanding and what research I’ve done (point is...take it for what it’s worth) is that definition has been around for as long as there’s been an immigration dept. So, not Obama admin thing.
Since it’s a constitutional question, it can’t be settled by any administration. Congress could settle it if they had the balls to pass a law and forbid the court to overrule it, subject to their authority do impose whatever “regulations and exceptions” on the courts’ jurisdition they choose. They have never done so. Otherwise only the courts can settle it.