Remember in May, when President Obama spoke about five categories of terrorism-related detainees for which his administration was creating or updating the legal architecture to process? Category two — detainees who “violate the laws of war and are therefore best tried through military commissions” — will be debated in the Senate this morning.

The military commissions created after 9/11 have had a vexed history. They provide for substantially less due process than military courts martial, which critics of the commissions contend are a preferable alternative for dealing with war criminals. One of them, a Navy lieutenant commander named Charlie Swift, litigated the point up to the Supreme Court in 2006 and won. Congress responded with the Military Commissions Act later that year — then-Senator Obama voted against it — but the Supreme Court struck down sections of that law in 2008, finding it to unreasonably restrict the right of habeas corpus. (Bonus fun fact: Justice Antonin Scalia, dissenting from the 5-4 ruling, warned that his colleagues’ decision would “almost certainly cause more Americans to be killed.” A year later, no one’s been killed because of the ruling.) At the National Archives in May, to the horror of civil libertarians, Obama confirmed that he indeed intended to revive the commissions process, and contended that he was neither a hypocrite nor a flip-flopper:

We will no longer permit the use of evidence — as evidence statements that have been obtained using cruel, inhuman, or degrading interrogation methods.  We will no longer place the burden to prove that hearsay is unreliable on the opponent of the hearsay.  And we will give detainees greater latitude in selecting their own counsel, and more protections if they refuse to testify.  These reforms, among others, will make our military commissions a more credible and effective means of administering justice …

Congress and the administration are exploring legislative pathways to enact those “reforms,” which remain vague and aspirational at the moment. And that’s what brings Jeh Johnson, the Pentagon’s general counsel; David Kris, the Justice Department’s national security chief; and Vice Adm. Bruce MacDonald, the Navy’s judge advocate general, before the Senate Armed Services Committee this morning. On June 26, the panel marked up the 2010 defense authorization bill, and included some language in it to restrict the use of “coerced testimony and hearsay evidence” in the commissions and ensure that convictions can “be upheld on appeal.” Expect the dialogue to expand on what this ought to mean in practice.

Hearing kicks off at 9:30 a.m.; to the blog I shall repair.