President Obama said on Sunday that now is the time “to start going on some offense” against the Islamic State in Iraq and Syria, or ISIS, the Sunni extremist group that is overrunning northern Iraq and has a stronghold in Syria. That would be a serious escalation of the American role there.

He will need to explain to the nation with specificity how airstrikes against ISIS in Syria fit into a broader strategy; how they could be successful; how they might be done without benefiting Syria’s dictator, Bashar al-Assad, who is under attack by ISIS and other Sunni opposition forces; and how the United States can avoid entanglement in another military morass if it moves more aggressively into this theater.
Until ISIS emerged as a regional threat, the Obama administration argued it had no legal standing to become militarily involved in Syria. American forces began airstrikes in August against ISIS fighters in Iraq after units of the Iraqi Army collapsed and extremists began persecuting minority groups, attacking the Mosul Dam and threatening Americans in Erbil. There seemed to be legal grounds for airstrikes because Iraq asked for assistance and Americans were at risk. From the beginning, Mr. Obama has pledged that ground troops would not be involved.

Administration officials now say Mr. Obama has authority to take action even across the porous Iraq-Syria border if there is intelligence identifying ISIS fighters in Syria involved in the beheadings of two American journalists or if requested to do so by the Iraqi government to protect its border.

Their assertion, however, does not resolve the question of the need for congressional authorization for military attacks in Syria. Lawmakers, facing re-election in November, seem divided on the need for a vote, although they will at least have to approve new financing for the mission. Mr. Obama himself has been ambiguous, saying in one breath, “I’m confident that I have the authorization that I need to protect the American people” and, in another, that Congress needs “to have buy-in” on the issue.

While most of the focus has been on military action, the administration’s strategy is broader, and those other elements — political, economic and diplomatic — are as important. On Monday, the Iraqis approved a new, more inclusive government, which the Americans pressed for and is essential to undercutting ISIS’s grip on disaffected Sunnis. There are plans for a new provincial force that would bring Sunnis and Shiite militias into Iraqi security structure and plans to train and equip moderate Syrian rebels so they can capitalize on airstrikes in Syria.
The Obama administration is also trying to marshal an international coalition to fight ISIS, but success is far from guaranteed. On Sunday, Arab League foreign ministers agreed to take necessary measures to confront ISIS, but they made no specific commitments. On Monday, a meeting between Defense Secretary Chuck Hagel and Turkish officials did not result in any firm announcement.

There are many ways for countries to make contributions, including shutting down channels for ISIS financing, closing Turkey’s border to ISIS fighters and weapons, urging Sunni tribes to work with the Shiite-led government in Baghdad, and providing intelligence to coalition members. But there are also many impediments and complications to getting disparate countries to work together, including Turkey’s fear that ISIS, in retaliation, might kill 49 Turkish diplomats held by the militants.

Mr. Obama has called ISIS a serious threat and has said, “we have the capacity to deal with it.” On Wednesday, he plans to give a speech about the issue. His challenge will be to persuade American and foreign listeners that he has an effective strategy to eliminate the threat.