The White House has an answer for critics who want to know how the Obama administration can justify striking ISIS inside Syria under international law: If and when we actually do it, we will come up with a legal justification then.

The Obama administration has explained at length why it believes it has the domestic legal justification for using airstrikes in Syria; they have claimed they don’t need Congressional authorization because the 2001 authorization for the use of military force against the perpetrators of 9/11 and the 2002 authorization to take down Saddam Hussein applies to the ISIS war. The New York Times called the explanations “perplexing” and insufficient. (After all, al Qaeda and ISIS have sporadically fought with one another, and the Saddam regime is long gone.)

But the administration has said almost nothing about why airstrikes in Syria would not be a direct violation of the international law of armed conflict and the United Nations charter, as both the Syrians and their Russian allies have claimed.

“Whenever the United States uses force in foreign territories, international legal principles, including respect for sovereignty and the law of armed conflict, impose important constraints on the ability of the United States to act unilaterally—and on the way in which the United States can use force,” National Security Council Spokesperson Caitlin Hayden told The Daily Beast. “With respect to international law, the specific basis will depend on the particular facts and circumstances related to any specific military actions, but we believe that we will have a basis for taking action.”

In the run up to the 2011 war in Libya, the Obama administration worked hard to secure a U.N. Security Council resolution authorizing NATO airstrikes against the Qaddafi regime. In 2013 when Obama planned to strike the Assad regime, the administration at least sought international endorsements from foreign parliaments, although the British parliament rejected Obama’s proposed strikes, before Obama pulled the plug on the idea.

In the war against ISIS, a non-state actor operating inside at least two sovereign states, Obama has been relying on the Iraqi government’s invitation as its legal rational for military action. But Baghdad would be hard pressed to extend that invitation to Syria.

The Obama administration is working through several possible legal justifications the administration could try to apply to airstrikes against ISIS inside Syria. But each is problematic and controversial in its own way. Sources close to the administration said the White House and its lawyers were still trying to figure out which justification they want to use. Experts are upset the White House doesn’t seem to be upholding the United States’ long held support for the adherence to international law when dealing with war.

“I’m disappointed in the level of supporting both domestic and international law in this military campaign. It’s important that the U.S. be seen as an adherent and supporter of international law and I’m concerned about the direction this is going,” said Ken Gude, senior fellow at the Center for American Progress, a think tank close to the administration that has supported the president’s anti-ISIS campaign in Iraq.

State Department Spokesperson Marie Harf on Sept. 11 rejected Russian and Syrian claims that a U.S. attack inside Syria would constitute a violation of international law and the UN charter. The international pact prohibits a violation of the territorial integrity of a UN member state (in this case, Syria) without that country’s permission or without a UN Security Council Resolution authorizing such use of force.

“I find it interesting that Russia’s suddenly taken an interest in international law, given some of their past behavior,” said Harf, in a not-so-subtle reference to the recent Russian invasion of Ukraine. “The President has the authority as Commander-in-Chief under the United States Constitution to take actions to protect our people. And any action we take overseas, of course, we will have an international legal basis for doing so. I don’t have predictions about what that is, given we haven’t announced additional actions yet.”

Harf implied that that the administration might claim the right to strike ISIS in Syria based on the principle of individual self-defense, a clear exception to the need for permission or UN Security Council. Such a rational might be applicable if the American government claims there’s an imminent threat to U.S. personnel in a state that is unwilling or unable to counter that threat. But if administration officials actually try to invoke individual self-defense as a justification, they would likely have to contradict repeated statements by top officials this week claiming ISIS does not present an immediate threat to the U.S. homeland.

Responding to Harf, Gude said the U.S. shouldn’t be gauging its adherence to international law against the adherence of Russia and Syria.

“In the aftermath of Russia’s clear violation of international law in Ukraine, we should be seen as committing further to the adherence of international norms, not undermining it,” he said. “What could happen here is that the norms that govern states’ application of force take a hit and those norms, largely enforced by the U.S. and that work together for the benefit of America and our allies, could be weakened.”

The Bashar al-Assad regime claims that it is willing to work with the American military inside Syria to fight ISIS, although Syrian officials have said in recent days that any U.S. attack inside its borders would be an act of aggression, unless it’s coordinated with the Damascus government. Secretary of State John Kerry ruled out coordinating with Assad inside Syria in a Sunday interview with CBS, although the U.S. will keep the Syrian government informed.

“We’re not going to coordinate with it Syria. We will certainly want to deconflict to make certain that they’re not about to do something that they might regret even more seriously,” Kerry said. “But we’re not going to coordinate. It’s not a cooperative effort. We are going to do what they haven’t done.”

Another possible international legal justification the administration might use is the right of “collective self defense,” under which the U.S. and its allies could claim that strikes inside Syria are part of the effort to defend the country of Iraq from ISIS. That justification would build on Kerry’s contention that the Assad regime is unable to control its own territory and therefore other states have a right to take action.

But this explanation has drawbacks as well. Namely, it would only justify actions to protect Iraq—not “destroy” ISIS, as President Obama has promised in recent days. Iraq would have to formally declare that it was threatened by ISIS forces in Syria, invoke its own right to self-defense, and then ask other states for assistance.

“This theory would limit the scope of action of those helping the Iraqi government: those providing assistance only could do so to the extent necessary to quell ISIS in Iraq and ensure that ISIS was unable to conduct future attacks there. The approach also would be contingent on Iraq’s consent, which it could withdraw,” former State Department lawyer and University of Virginia Law School Professor Ashley Deeks wrote on the Lawfare blog. “As a political matter, it seems doubtful that the United States would find this to be an appealing approach, particularly if it perceives its own national interests to be at stake.”

A third possible international legal justification by the Obama administration could be to invoke the same justification it is now using to explain the ISIS war on domestic legal grounds, the principle that the war against al Qaeda is an ongoing armed conflict and that ISIS is part of al Qaeda. That argument must be reconciled with the fact that ISIS and al Qaeda are publicly at war with each other and fighting on the ground every day in Syria.

Of course, the U.S. could also pursue a UN Security Council resolution during the meeting President Obama will chair in New York next week, a follow on to UNSC Resolution 2170 on ISIS, passed last month, which did not authorize the use of force. But Russia is sure to veto that effort.

Former UN official Hardin Lang, also a senior fellow at CAP, said that even if there is no international consensus on striking inside Syria, the U.S. must confront the issue of international legal justification openly and honestly if it wants to build and maintain a regional and international coalition for fighting ISIS over the long term, wherever it may move next.

“We are getting close to a moment in terms of our international position where questions will be raised about, ‘How is what you are doing any different from what was done is some other historical examples we are not as proud of,’” he said. “We need to make the effort, although we shouldn’t be wholly constrained by that.”