U.S. Defense Secretary Chuck Hagel says U.S. forces are ready to launch strikes on Syria if President Barack Obama decides to order military action, and a major U.S. news outlet is reporting that a strike could happen within days.
"The options are there. The United States Department of Defense is ready to carry out those options," Hagel told the BBC. "If that would occur, that would occur also in coordination with our international partners."
What is U.S.-led military intervention likely to look like?
A senior administration official told Reuters on August 27 that the U.S. president had not made a decision.
But NBC News quoted unnamed senior administration officials as saying that plans were in place for a missile strike inside Syria and that "three days" of strikes could begin as early as August 29.
The U.S. Navy has four destroyers in the Mediterranean within range of Syria. They carry Tomahawk missiles, which can "circle for hours and shift course instantly on command," according to their manufacturer, Raytheon.
Barry Pavel, who was senior director for defense policy and strategy at the National Security Council under Obama and former President George W. Bush and is now at the Atlantic Council, says air strikes are also possible.
"My best and most informed speculation would be this would be an air campaign which would involve a combination of cruise-missile strikes and air strikes," Pavel says. "The targets, duration, and intensity and timing of the campaign would be largely driven by the particular mission objectives that the president directs the military to carry out."
The White House said on August 27 that the options being considered "are not about regime change."
What about establishing a no-fly zone over rebel-held areas, like NATO allies did in Libya?
It would be difficult to gain control of Syrian airspace. The Syrian Air Force is formidable -- much stronger than Libya's was. The risk of U.S. planes being shot down is one the White House doesn't want to take. After two lengthy wars, this has to be a bloodless engagement.
The closest U.S. warplanes are at Turkish air bases. Sorties from air bases in Persian Gulf countries would be harder; Jordan and Iraq say they won't let U.S. planes into their airspace.
The United States could also use B-2 stealth bombers, which have a range of 11,100 kilometers and are able to evade heavy antiaircraft defenses.
Would U.S. troops be involved?
Disabling chemical-weapons depots by firing missiles at them isn't an option. But sending in ground troops to do the job isn't either.
"Certainly, nobody is advocating boots on the ground, I'm not. And no one I know who's serious is advocating boots on the ground," says Representative Eliot Engel, the ranking Democrat on the House Foreign Affairs Committee, whom Secretary of State John Kerry consulted with on August 26.
"There are lots of things that we can do to degrade Assad's air force, to have cruise missiles come in from outside of Syria, destroy the runways so he cannot launch an air attack upon his own people, to destroy his weapons and munitions depots, and oil and fuel [depots]," Engels adds.
"There are things that we can do short of going to war or having boots on the ground, so nobody is talking about going to war or having boots on the ground."
What are the U.S. arguments for and against military intervention?
The argument for military action is to put a stop to what the world long ago agreed should never happen: chemical warfare.
The Atlantic Council's Pavel says missile strikes "would be the first time since the conflict began that the United States would be giving Assad a negative incentive" to continue.
Engel says it might also tilt the balance of the Syrian war, which he says would be "a good thing."
The argument against involvement is the risk of "mission creep" -- the potential for the United States to get pulled into another war.
Would the U.S. go it alone?
Western allies are weighing in on the Syria issue, with some expressing readiness to take action. Whether that includes military action is another matter.
French President Francois Hollande said this week that "France is ready to punish those who took the heinous decision to gas innocents," without elaborating. Earlier he listed several options, including arming rebel forces, conducting air strikes, or the imposition of economic sanctions. Hollande has pledged support to the United States in the event of a targeted military intervention.
The United Kingdom is preparing contingency plans for military action in Syria as it continues to sort through "a range of evidence" including that gathered from UN weapons inspectors. The United Kingdom has stressed that any response would be proportionate, within international law, and carried out in cooperation with allies.
British Prime Minister David Cameron, who has said the use of chemical weapons "cannot stand," has the final say on the use of force. Cameron has recalled Parliament from summer recess to discuss a possible military response. The session will be held on August 29.
German Chancellor Angela Merkel participated in a telephone conference with the French, U.S., and U.K. leaders in which they agreed on the need for a "serious response." Military action is among the options reportedly discussed. However, elections that could keep Merkel in office are just weeks away, and voters overwhelmingly oppose a military strike against Syria (69 percent of Germans according to an August 27 poll). Opposition parties have rejected resorting to the use of force unless it can be proved the Syrian regime was behind the attack.
Turkey has been a leading critic of the Syrian regime since the conflict began more than two years ago. This week, Turkish Foreign Minister Ahmet Davutoglu said that "those who commit war crimes and crimes against humanity must definitely be punished." He said that "36-37 countries" are discussing alternatives and, if a coalition is formed, Turkey would join, with or without UN approval.
Where is the United Nations in all this?
Security Council member Russia is an Assad ally and would likely veto any attempt to authorize military action. So would China.
To build its legal case, the White House is studying the "Kosovo precedent" -- the 1999 NATO-led bombing campaign that drove Yugoslav President Slobodan Milosevic's forces out of Kosovo but did not have UN authorization.
The U.S. secretary of defense at the time, William Cohen, and others defended the campaign's legality by saying international norms had been violated and "this is a fight for justice over genocide."
On August 26, Kerry said: "There is a reason why President Obama has made clear to the Assad regime that this international norm cannot be violated without consequences."
How might Syria's allies, Russia and Iran, respond?
U.S. hesitation about getting involved in Syria has long been partly out of the worry that it would spark a proxy war with Russia.
Pavel says those worries are now irrelevant. "Let's be truthful here: we're in a proxy war," he says.
"And one of the reasons that the administration said, in July 2011 -- when there was some pressure to intervene -- one of the reasons they used to not intervene was that they didn't want to overmilitarize the conflict and get others to increase the flow of military equipment and advisers to Syria," he continues. "Well, that's happened already. It's been happening for two years. Iran is all in. Russia is in to a degree."
He says he doesn't believe Moscow would join the battle if the United States launched a limited military strike aimed solely at deterring future chemical-weapons use.
After all, Russia is a signatory to the Chemical Weapons Convention, which outlaws their use. Syria is not.