Is it a response to a potential genocide or an opening to take on the Sunni Islamic extremists rampaging through Iraq?
President Barack Obama's decision to authorize airstrikes escalated American military involvement in Iraq, a country he tried to get out of more than two years ago.
The first U.S. attacks happened Friday, with F/A-18 jets bombing mobile artillery batteries of ISIS, which refers to itself as the Islamic State.
While the administration adamantly reassures Americans that it won't put U.S. boots on the ground, it also has made a compelling case for going after the ISIS threat.
1. Signs of genocide
Obama and the U.N. High Commissioner for Human Rights talk of potential genocide and crimes against humanity if ISIS fighters slaughter minority groups fleeing them in the north.
In particular, tens of thousands of Yazidis, a religious minority in the north, have fled into mountains where they lack food and services and remain vulnerable to the ISIS rampage.
"Convert to Islam or die" is the ISIS ultimatum, as given to Christians when the group overran that minority's largest city, Qaraqosh.
A senior U.S. administration said ISIS backs up its threat by beheading people with differing religious convictions and putting the heads on spikes to terrorize others.
The militants' carnage has displaced hundreds of thousands of people, especially from Iraq's second-largest city, Mosul. In addition, thousands of Yazidi families are stranded, and two U.S. military cargo planes airdropped 5,300 gallons of water and 8,000 meals to them Thursday.
U.S. Secretary of State John Kerry warned that ISIS' "grotesque and targeted acts of violence bear all the warning signs and hallmarks of genocide."
2. Protect U.S. interests and personnel
"We do whatever is necessary to protect our people," Obama said Thursday night in announcing his authorization of airstrikes. "We support our allies when they're in danger."
Those two principles sum up the reasons for what he did.
There are hundreds of military personnel in Iraq, many of them advisers sent to work with Iraqi and Kurdish military officials in response to the ISIS threat.
Dozens of them are in Irbil, the largest city of the Kurdish region, which has been one of the most stable regions in Iraq and a cooperative U.S. partner. U.S. consular staff are there with them.
Friday's initial airstrikes hit ISIS artillery outside Irbil, according to the Pentagon.
Kurdish officials say their fighting force, the Peshmerga, can hold off an ISIS advance, but the militants have weapons taken from Iraqi forces in areas they've already overrun.
3. Take on the extremists
Obama continues pushing for a political solution in Iraq, saying U.S. military action can't solve the conflict.
But when asked why the United States was not evacuating American personnel, a senior administration official said the United States has the wherewithal to protect them and prefers instead to "lay down a marker" before ISIS.
Hawkish critics in Washington agree the United States doesn't want another war in Iraq, but they say America can do more.
"Degrade ISIS" was the dictum from Republican Sens. John McCain of Arizona and Lindsey Graham of South Carolina. "It is inherently expansionist and must be stopped."
They suggest a take-it-to-them formula: Arm all partners who fight ISIS, including in Syria, and bomb their leaders, troops and positions, including in Syria.
The Obama administration has pushed for Iraqis to form a new government more representative of Iraq's Sunni Muslims than currently exists under Prime Minister Nuri al-Maliki. Many disaffected Sunni Muslim have joined ISIS.
Then the White House wants Iraqi military forces to handle the threat.