Paul Starobin is the author of “After America: Narratives for the Next Global Age.”

HAROLD HONGJU KOH, the former dean of the Yale Law School, has been one of the country’s foremost defenders of the notion that the president of the United States can’t wage wars without the approval of Congress. During the Bush administration, he was legendary for his piercing criticisms of “executive muscle flexing” in the White House’s pursuit of the so-called war on terror.

Even more, he was described by those who knew him as the inspiration for a generation of human rights activists and lawyers passionately committed to a vision of a post-imperial America as a model of constitutional restraint. His colleagues viewed him as not only a brilliant scholar but a “liberal icon.”

Suddenly, though, Mr. Koh seems to be a different person.

Just over two years ago, he became legal adviser to Hillary Rodham Clinton’s State Department, and in that job, he has become the administration’s defender of the right to stay engaged in a conflict against Libya without Congressional approval. He argues that the president can proceed because the country is not actually engaging in “hostilities.” Because “hostilities” is “an ambiguous standard,” he has argued, the president need not withdraw forces to meet the resolution’s requirement of an automatic pull-out, 60 days after “hostilities” begin, absent express Congressional approval for the war. The conflict is in its fourth month, and no such consent has been given.

Mr. Koh’s allies, speaking more in sorrow than in anger, are mystified and disheartened to see their hero engaging in legalistic “word play.” To them, it’s as if he has torn off his team jersey, midgame, and put on the other side’s. Mary Ellen O’Connell, a Notre Dame law professor who has known Mr. Koh for a quarter-century, is seeking an answer to this question: “Where is the Harold Koh I worked with to ensure that international law, human rights and the Constitution were honored during the Bush years?”