The U.S. Senate grilled State Department legal advisor Harold Koh on Tuesday as he defended the Obama administration’s claim that the War Powers Resolution, passed in the wake of Vietnam in 1973 to prevent extended overseas military action without Congressional approval, does not apply to the Libya incursion.

The Act says that within 60 or 90 days after informing Congress of hostilities, military action must cease without the go-ahead from lawmakers.

“From the outset, we noted that the situation in Libya does not constitute a war,” Mr. Koh said, calling the phrase “hostilities” an “ambiguous word of art” that did not likely apply in Libya.

Indiana Republican Senator Dick Lugar, an Obama ally who worked with him on nuclear issues when they were both senators and who led efforts to corral GOP votes for renewal of the START treaty with Russia last winter, was critical.

“Presidents should not be able to avoid constitutional responsibilities merely because engaging the people’s representative is inconvenient or uncertain,” he said.

Virginia Senator Jim Webb, whom Obama campaigned for in 2006 and who returned the favor in the fall of 2008, when Obama won his state, was perhaps the most outspoken, despite being a member of the president’s party.

“When you have an operation that goes on for months, costs billions of dollars, where the United States is providing two-thirds of the troops, even under the NATO fig leaf, where they’re dropping bombs that are killing people, where you’re paying your troops offshore combat pay and there are areas of prospective escalation — something I’ve been trying to get a clear answer from with this administration for several weeks now, and that is the possibility of a ground presence in some form or another, once the Qaddafi regime expires — I would say that’s hostilities,” he said. [The New York Times]