It's Unlikely, But Worth Noting:
In today's debates on Boumediene v. Bush, I think it's worth noting that there's a way in which Congress could still go back to the pre-Rasul or pre-Boumediene state of the law: Congress could formally suspend the Writ as it applies to Guantanamo Bay. The Suspension Clause does not require the writ of habeas corpus; rather, it states that "[t]he Privilege of the Writ of Habeas Corpus shall not be suspended, unless when in Cases of Rebellion or Invasion the public Safety may require it." (emphasis added)

  As far as I know, the Court has never analyzed whether the "public safety" exception is justiciable or is a political question, or what standards could apply to judicial review of it. (See my colleague Amanda Tyler's article, Is Suspension a Politcal Question?, for more.) But if the political branches wanted to go back one more time, they could, subject to the possibility of judicial review of their assessment of the need for the suspension. To be clear, I'm not recommending this; and I think it's extremely unlikely that it would happen for political reason. But I think it's worth noting that it's possible.