WASHINGTON – The past 72 hours have been marked by a dramatic escalation in rhetoric from the White House on Syria, strongly implying that an attack on the assets of its nominal president, Bashar Assad, is imminent.Multiple crisis meetings in the Oval Office, stern warnings of warship movements in the Mediterranean from the Pentagon, and strategically leaked US intelligence findings on mass chemical weapons use in the Damascus suburb of Ghouta on Wednesday all made for a clear and consistent drumbeat toward action, despite President Barack Obama’s hesitancy to intervene throughout two years of the conflict. A senior US official said that shelling of the site on Thursday, and the time that had passed since, made the investigation “too late to be credible.”That statement implied the US was planning to move forward with allies Britain and France with alternative measures. British press outlets reported that a half-hour phone call between Prime Minister David Cameron and the US president on Saturday focused on military, not diplomatic, options.Those options are extensive, but the US is likely to strike in a limited, determined and surgical manner. The president’s target list includes Assad government command and control centers, airstrips and control towers, arms and artillery caches, fuel sources and mobile military units such as tank brigades.Striking airstrips would hinder Assad’s ability to import resources for his war effort from Iran. But they would have a limited effect: airstrips are easily repaved, and the president is unlikely to see this operation as a protracted effort.Instead, the US is more likely to strike significant permanent facilities central to the operations of Assad’s army, perhaps including targets the administration can cite as directly linked to Assad’s chemical weapons program.The US and its allies, if they choose to participate, will almost certainly use standoff strike capabilities: missiles from afar, fired from ships in the Mediterranean, as opposed to strikes from fighter jets that would have to enter foreign air space.Four US Navy craft have been positioned within range of potential targets in Syria equipped with over 100 Tomahawk missiles, which cost $1.4 million each.The US will be unable to cite self-defense as a legal argument for intervention.But they might cite an international norm called the “responsibility to protect,” or R2P.International law bans the use of chemical weapons on any battlefield under any circumstances. And R2P – a norm agreed upon by global powers at the United Nations 2005 World Summit – compels the international community to respond if a country fails to protect its citizens from genocide, war crimes, ethnic cleansing or crimes against humanity.Russia agreed to the principles of R2P at the summit, and cited R2P during its campaign in Georgia in 2008.The US would not be the first country to conduct direct strikes in Syria since the country’s civil war began over two years ago. Israel has conducted several air strikes against Syrian targets that its government has deemed direct threats to Israel’s national security, including heavy weapons shipments to Hezbollah in Lebanon from Iran.The clearest sign yet was the Obama administration’s quick dismissal of Syria’s decision to grant UN inspectors access to the site of Wednesday’s attack.