Benjamin Wittes is a senior fellow at the Brookings Institution and a member of the Hoover Institution’s Task Force on National Security and Law. He will be covering the KSM arraignment for the Lawfare Blog.

When Khalid Sheik Mohammed and four others are arraigned Saturday in a military commission at Guantanamo Bay on charges of orchestrating the Sept. 11, 2001, attacks, it will be the public’s first glimpse in several years of the 9/11 mastermind. The event holds the promise of long-delayed justice and will renew debate over the interrogations of the operation’s key planners.

But the arraignment represents more than the possibility that we might hear once again from the flamboyant and mesmerizingly evil KSM. It is also likely to serve as a make-or-break test for the military commissions system, a system in which the Obama administration has — despite its initial instincts and ongoing misgivings — invested considerable prestige and energy.

I have sat through every minute of every recent commission hearing, and the system looks nothing like the kangaroo court of human rights groups’ caricatures. The media will no doubt have a field day if KSM makes things unruly Saturday — as he very well might — but any spectacle should not obscure a larger truth about the tribunals in which he and his co-defendants will face trial: Quietly and gradually, the commissions have become a real court.

More than a decade ago, the Bush administration launched the military commission system on the theory that commissions would deliver swift, streamlined justice for major terrorist figures. But the commissions’ development was stunted by a combination of early structural and legal flaws, litigation, staffing and personnel problems, and, at times, inadequate political commitment and attention. Despite the commissions’ obvious underperformance, however, opponents never succeeded in killing off the system. Even as the commissions foundered, Congress repeatedly insisted on their availability, and sometimes primacy, for certain kinds of cases. (In one bill the House passed last year, for example, Congress sought to require the use of commissions in all terrorism cases involving foreign nationals.)

The result has been a peculiar stalemate in which the commissions have been allowed to neither succeed nor fail.

This weekend’s arraignment marks the beginning of the third major effort to bring the 9/11 conspirators to justice. The Obama administration dropped earlier military-commission charges against them when it decided in late 2009 to bring the 9/11 case to federal court in New York. But Congress, not wanting Guantanamo detainees brought to the United States, blocked the civilian trials. Meanwhile, the administration’s own view of the institution was evolving. When President Obama first took office, he froze commission proceedings with the apparent intention of shutting them down. But later that year the administration shifted gears and worked with Congress to make small but important adjustments to the Bush-era Military Commissions Act. These left commission proceedings more closely resembling the norms of a federal court trial.

The result of Congress’s interference in the 9/11 case was that if the administration wanted to try the conspirators at all, military commissions were its only option. But by this point, the administration’s problems with the commissions had been considerably ameliorated.

So the administration awkwardly embraced commissions — upsetting the president’s political base and causing discomfort among administration officials, some of whom don’t believe in the commissions’ necessity or in the inadequacy of federal courts for counterterrorism cases.

The president doesn’t talk much about commissions, yet his administration’s support for this trial venue has produced tangible and promising results. Today the commissions’ prosecution and defense sides have first-rate staff. Cooperation between the Defense and Justice departments — where much of the expertise for complex counterterrorism prosecutions resides — has been greatly enhanced. The military judge who has presided at recent cases and is scheduled to preside Saturday would do credit to any federal trial court in the country.

In short, there is reason to be optimistic that the long effort to bring the 9/11 conspirators to trial will finally succeed. A failure this time probably would — and certainly should — spell the end of the commissions experiment. This was an institution created for this type of trial. It has no reason for being if it is not up to the task.

But the talent, resources and energy poured into the system in recent years make a successful trial the more likely outcome. And success would raise its own questions about the commissions’ future: what role, if any, the public wants them to play down the line.

This will be a deeply uncomfortable issue for those who oppose the commission system absolutely and want to see it shuttered. The answer is not obvious even for those of us who do not object to the institution as a matter of principle. Is this to be a Nuremberg-like tribunal that is set up to try a particular set of crimes and that will fade away afterward? Is it — as the Obama administration has intimated — a court that has a plausible, though narrow, role in the future for terror acts with a particularly military character? Or is it to be, as Congress has more ambitiously intimated, the preferred venue for terrorism cases against foreign nationals in general?

The right answer is that successful commissions probably do have some narrow prospective role, and we’re going to have to think hard about what that role looks like.

This weekend, we’ll begin to find out just how far this institution has come — and whether it has come far enough.