Attorney General Eric Holder’s decision to try Sept. 11 terrorist mastermind Khalid Sheik Mohammed and his four co-conspirators in military tribunals is the clearest example yet of how a campaign promise can be obliterated by governing reality. As a candidate, then-Sen. Barack Obama (D-Ill.) promised to shut down Guantanamo Bay and end military commissions. Now that he’s president, Obama has had to go back on his pledge. It wasn’t for lack of trying — or meddling by Congress.

Obama made the promise in a speech on Aug. 1, 2007. (Forgive the web cache. If you try to go to the speech now, it takes you to Obama’s reelection site. Clever.)

I also will reject a legal framework that does not work. There has been only one conviction at Guantanamo. It was for a guilty plea on material support for terrorism. The sentence was 9 months. There has not been one conviction of a terrorist act. I have faith in America's courts, and I have faith in our JAGs. As President, I will close Guantanamo, reject the Military Commissions Act, and adhere to the Geneva Conventions. Our Constitution and our Uniform Code of Military Justice provide a framework for dealing with the terrorists.

Announcing the reversal of that promise and abandoning efforts to try KSM in the United States, Holder said, “Had this case proceeded in Manhattan or in an alternative venue in the United States, as I seriously explored in the past year, I am confident that our justice system would have performed with the same distinction that has been its hallmark for over two hundred years.”

I totally agree with Holder and with candidate Obama. I can’t understand how the “America is exceptional” crowd can’t bear to let the Constitution uphold the ideals we proudly profess to other nations. Instead, Congress blocked the administration from bringing any Guantanamo detainee to American soil for any reason.

As today’s Post editorial notes, Holder and the administration didn’t handle the initial decision to try KSM in Lower Manhattan very well. But it goes on to highlight the stark choice facing Obama and Holder going forward.

The administration’s remaining choice was not between a federal court trial and a military commission for the Sept. 11 defendants but between charging the men in the military system and holding them indefinitely without trial.

The editorial notes that the military commissions have many of the legal protections provided in civilian courts. So, at least some American ideals will be sustained at trial. As the editorial argues, the administration is “mak[ing] the best of a less than ideal situation.”