WASHINGTON — In asking Congress to authorize an attack on Syria over claims it used chemical weapons, President Obama has chosen to involve lawmakers in deciding whether to undertake a military intervention that in some respects resembles the limited types that many presidents — Ronald Reagan in Grenada, Bill Clinton in Kosovo and even Mr. Obama in Libya — have launched on their own.
On another level, the proposed strike is unlike anything that has come before — an attack inside the territory of a sovereign country, without its consent, without a self-defense rationale and without the authorization of the United Nations Security Council or even the participation of a multilateral treaty alliance like NATO, and for the purpose of punishing an alleged war crime that has already occurred rather than preventing an imminent disaster.
The contrasting moves, ceding more of a political role to Congress domestically while expanding national war powers on the international stage, underscore the complexity of Mr. Obama’s approach to the Syrian crisis. His administration pressed its case on Sunday, saying it had won Saudi backing for a strike, even as the Syrian president warned he would retaliate.
Mr. Obama’s strategy ensures that no matter what happens, the crisis is likely to create an important precedent in the often murky legal question of when presidents or nations may lawfully use military force.
Kathryn Ruemmler, the White House counsel, said the president believed a strike would be lawful, both in international law and domestic law, even if neither the Security Council nor Congress approved it. But the novel circumstances, she said, led Mr. Obama to seek Congressional concurrence to bolster its legitimacy.
The move is right, said Walter Dellinger, who led the Justice Department’s Office of Legal Counsel in the Clinton administration, because the proposed attack is not “covered by any of the previous precedents for the unilateral use of executive power.”
“That doesn’t mean it couldn’t become another precedent,” Mr. Dellinger added. “But when the president is going beyond where any previous president has gone, it seems appropriate to determine whether Congress concurs.”
Disputes about whether and when a president or nation may launch an act of war can be hazy because courts generally do not issue definitive answers about such matters. Instead presidents, and countries, create precedents that over time can become generally accepted as a gloss on what written domestic laws and international treaties permit. Against that backdrop, many legal scholars say Mr. Obama is proposing to violate international law. But others contend that the question is ambiguous, and some suggest that the United States could establish a precedent creating new international law if it strikes.
The United States has used its armed forces abroad dozens of times without Security Council approval, but typically has invoked self-defense; when Mr. Reagan invaded Grenada in 1983, for example, he cited a need to protect Americans on the island along with the request of neighboring countries. The most notable precedent for the Syria crisis was Mr. Clinton’s 1999 bombing of Kosovo, but that was undertaken as part of NATO and in response to a time-urgent problem: stopping a massacre of civilians.
By contrast, the United States would carry out strikes on Syria largely alone, and to punish an offense that has already occurred. That crime, moreover, is defined by two treatiesbanning chemical weapons, only one of which Syria signed, that contain no enforcement provisions. Such a strike has never happened before.
Attempts to deal with the novelty of the crisis in international law have become entangled in the separate domestic law question of whether the president could order strikes on Syria without Congressional permission.
Seeking the 2008 Democratic presidential nomination, Mr. Obama embraced a limited view of a president’s power to initiate war without Congress, telling The Boston Globe that “the president does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation.”
But by the 2011 conflict in Libya he abandoned his campaign view of presidential war powers as too limited. While the NATO intervention was authorized for international law purposes by the Security Council, in domestic law Congress did not authorize Mr. Obama to participate. But Mr. Obama’s Office of Legal Counsel argued that it was lawful for him to unilaterally order American forces to bomb Libya because of national interests in preserving regional stability and in supporting the “credibility and effectiveness” of the Security Council.
In recent weeks, administration lawyers decided that it was within Mr. Obama’s constitutional authority to carry out a strike on Syria as well, even without permission from Congress or the Security Council, because of the “important national interests” of limiting regional instability and of enforcing the norm against using chemical weapons, Ms. Ruemmler said.
But even if he could act alone, that left the question of whether he should. The lack of a historical analogue and traditional factors that have justified such operations, she said, contributed to his decision to go to Congress.
“The president believed that it was important to enhance the legitimacy of any action that would be taken by the executive,” Ms. Ruemmler said, “to seek Congressional approval of that action and have it be seen, again as a matter of legitimacy both domestically and internationally, that there was a unified American response to the horrendous violation of the international norm against chemical weapons use.”
At a news conference last week, Mr. Obama argued that the United States should “get out of the habit” of having the president “stretch the boundaries of his authority as far as he can” while lawmakers “snipe” from the sidelines. But he also explained his decision in terms of very special circumstances: humanitarian interventions where there is no immediate pressure to act and the United Nations is blocked.
Jack Goldsmith, a head of the Office of Legal Counsel in the Bush administration, said the limited criteria cited by Mr. Obama mean his move might not apply to more traditional future interventions. The more important precedent, he said, may concern international law and what he portrayed as Mr. Obama’s dismissive attitude toward whether or not having permission from the Security Council should stop humanitarian interventions.
Mr. Obama has in recent days repeatedly portrayed the Security Council system as incapable of performing its function of “enforcing international norms and international law,” and as so paralyzed by the veto power wielded by Russia that it is instead acting as a “barrier” to that goal.
Mr. Goldsmith said that in the Kosovo campaign, the Clinton administration shied away from arguing that it was consistent with international law to carry out a military attack not authorized by the Security Council purely for humanitarian reasons. Its fear was that such a doctrine could be misused by other nations, loosening constraints on war.
In his 2009 Nobel Peace Prize acceptance speech, Mr. Obama said all nations “must adhere to standards that govern the use of force.” But he also argued that humanitarian grounds justified military force and cited “the Balkans,” leaving ambiguous whether he meant Bosnia, which had some Security Council approval; Kosovo, which did not; or both.
Ms. Ruemmler said that while an attack on Syria “may not fit under a traditionally recognized legal basis under international law,” the administration believed that given the novel factors and circumstances, such an action would nevertheless be “justified and legitimate under international law” and so not prohibited.
Still, she acknowledged that it was “more controversial for the president to act alone in these circumstances” than for him to do so with Congressional backing.
Steven G. Bradbury, a head of the Office of Legal Counsel in the Bush administration, said it would be “politically difficult” to order strikes if Congress refused to approve them. But he predicted future presidents would not feel legally constrained to echo Mr. Obama’s request. “Every overseas situation, every set of exigent circumstances, is a little different, so I don’t really buy that it’s going to tie future presidents’ hands very much,” he said.
But Harold H. Bruff, a University of Colorado law professor who is one of the authors of a casebook on the separation of powers, argued that the episode would have enduring political ramifications. “I’m sure that Obama or some later president will argue later that they can still choose whether or not to go to Congress,” he said. “But it does raise the political cost of a future president not going to Congress because the precedent will be cited against him or her.”