Several prominent constitutional law scholars from across the political spectrum have denounced President Obama’s decision to launch a military campaign against ISIS without congressional authorization. My own critique of the president’s actions is almost an apologia for the White House compared to the commentaries by famous liberal constitutional law scholar Bruce Ackerman, conservative Harvard professor Jack Goldsmith (a leading expert on national security law became famous when he repudiated the “torture memo” while serving in the Bush administration), war powers expert Lou Fisher, and Benjamin Wittes of the center-left Brookings Institution.

Ackerman’s critique is perhaps the toughest of the lot. Although Ackerman was one of my mentors in law school, he and I don’t agree on major constitutional law issues particularly often. This case is an exception:

President Obama’s declaration of war against the terrorist group known as the Islamic State in Iraq and Syria marks a decisive break in the American constitutional tradition. Nothing attempted by his predecessor, George W. Bush, remotely compares in imperial hubris.

Mr. Bush gained explicit congressional consent for his invasions of Afghanistan and Iraq. In contrast, the Obama administration has not even published a legal opinion attempting to justify the president’s assertion of unilateral war-making authority. This is because no serious opinion can be written.

This became clear when White House officials briefed reporters before Mr. Obama’s speech to the nation on Wednesday evening. They said a war against ISIS was justified by Congress’s authorization of force against Al Qaeda after the Sept. 11, 2001, attacks, and that no new approval was needed.

But the 2001 authorization for the use of military force does not apply here. That resolution — scaled back from what Mr. Bush initially wanted — extended only to nations and organizations that “planned, authorized, committed or aided” the 9/11 attacks….

Not only was ISIS created long after 2001, but Al Qaeda publicly disavowed it earlier this year. It is Al Qaeda’s competitor, not its affiliate.

When one of the nation’s most famous liberal constitutional law professors not only compares Obama to Bush, but actually concludes that Obama is much worse, them’s fightin’ words!

At some points, I think Ackerman goes farther than is justified in claiming that the ISIS campaign is unprecedented. For example, he argues that it is more clearly illegal than the 2011 war against Libya (which Ackerman also criticized), because the former cannot be defended on the basis that the United States is “leading from behind.” But while it is true that Britain and France took the lead in the Libya air campaign, non-American forces such as the Kurds, Iraqi government forces, and others are doing the lion’s share of the fighting against ISIS too. In any event (as Ackerman would agree), “leading from behind” cannot justify an otherwise illegal military intervention. Whether the US is in a conflict that qualifies as a war requiring congressional authorization depends on what the president orders American forces to do, not on the number of allied forces that might also be involved in the fighting. Otherwise, Woodrow Wilson could have argued that US entry into World War I did not require congressional authorization. After all, the British and French contributed more troops and suffered far greater losses than the US military did in that conflict.

Secretary of State John Kerry has attempted to defend the administration’s actions by claiming that the campaign is not a war:

U.S. Secretary of State John Kerry on Thursday would not say the United States is at war with ISIS, telling CNN in an interview that the administration’s strategy includes “many different things that one doesn’t think of normally in context of war.”

“What we are doing is engaging in a very significant counterterrorism operation,” Kerry told CNN’s Elise Labott in Jeddah, Saudi Arabia. “It’s going to go on for some period of time. If somebody wants to think about it as being a war with ISIL, they can do so, but the fact is it’s a major counterterrorism operation that will have many different moving parts.”

This argument is no more persuasive than Kerry’s attempt, last year, to explain why Obama’s 2011 bombing of Libya had a better legal justification than Richard Nixon’s bombing of Cambodia. Among other things, “war” and “counterterrorism” are not mutually exclusive categories. Counterterrorism campaigns can and do involve enough large-scale fighting to qualify as a war. The campaign against al Qaeda (which the president himself has described as a war) is a good example. And it’s pretty obvious that many wars have “many different moving parts.”

However, hope is not yet lost for the administration. At least one famous legal academic has offered a stronger defense for its actions than that provided by the Secretary of State. Given Obama’s earlier record as a staunch critic of abuses of executive power in the Bush administration, I am not sure that he is especially happy to have John Yoo as one of his most articulate defenders. Still, Yoo’s arguments are worth serious consideration, and I will try to address them in my next post.

UPDATE: Since I originally wrote this post, other administration officials have contradicted Secretary of State John Kerry’s statement that the conflict with ISIS is not a war. It is possible that Kerry’s claim does not represent the administration’s official position. But if the administration really does consider the conflict to be a war, that strengthens the case for adhering to the requirement of congressional authorization.