With the Justice Department’s release of the criminal charges that could be brought against an American fighting for the Taliban, the case of John Walker begins a necessary and inevitable transformation. The initially all-consuming question of why this son of affluence went to war against his county for a barbarous cause becomes less important than proving, according to the rules of evidence and the concept of due process, precisely what he did after the war began.

The potential charges, though they could apply generally to any American Taliban, clearly apply specifically to Mr. Walker, the only American known to be in this self-inflicted danger. They range from treason and murder, death-penalty offenses, to conspiracy and – the charge Justice suggests might be the most promising – providing material support to terrorists.

If nothing else, Mr. Walker certainly is guilty of bad timing. After the Sept. 11 attacks, Congress elevated the maximum penalty for the material support crime from 10 years in prison to 15, and to life if that support resulted in a death. He will, of course, have to answer for the death of CIA agent Mike Spann, murdered in the Mazar-e-Sharif prison uprising just hours after Mr. Spann tried to interview the uncooperative prisoner, but, unlike the murder charges, the material support law does not apply only to the death of a U.S. citizen.

The ultimate decision on what Mr. Walker will be charged with and in what venue he will be prosecuted lies with President Bush, who promises to consider the matter deliberatively and judiciously. Those are the virtues that have guided Mr. Bush successfully thus far on this issue and are especially needed now.

The decision on the charges will be made in consultation with Justice Department prosecutors and no good prosecutor ever brings a charge that won’t lead to a conviction. Given Mr. Walker’s apparent lack of remorse and the pitiful cluelessness of his parents, public outrage likely will run high if the decision is not to bring a treason charge, higher still if a plea bargain – a very real possibility – is worked out and a trial is avoided. Either outcome will test severely the president’s persuasive skills.

Should Mr. Walker go to trial, the decision on venue is more political. It has been suggested that Mr. Walker be stripped of his American citizenship and tried by a military tribunal. The president should reject that suggestion – from the moment American forces took custody of Mr. Walker from Afghan troops, the implicit understanding has been that Mr. Walker was being treated differently from other captured Taliban because he is an American citizen. This was the correct approach and should be continued. There can, in fact, be no more powerful way to demonstrate to the world the difference between being an American and being a Taliban.