A U.S. missile strike on Syria could trigger an explosive chain reaction involving from Syria or its allies like Hezbollah and Iran, and the blowback could hit U.S. targets or Israel, experts told ABCNews.com.
Or Syria might simply stop using chemical weapons and there could be no retaliation at all.
Gauging the ripple effect of a U.S. strike on Syria is part of the calculations of the Obama administration, but it is an imprecise science.
"When you do a military strike it often has ramifications you don't anticipate," said Dan Byman, a senior fellow of foreign policy at Brookings Institute.
- Syrian President Assad accused of using chemical weapons on citizens.
- President Obama called chemical weapons a "red line" that Assad crossed.
- U.S. says it is "ready to go" for strike on Syria.
Here are five scenarios the the U.S. could face in coming weeks.
1. Syria Will Try to Retaliate
Syria has already made bold threats toward the U.S. and its allies, specifically Israel, about retaliation for any U.S. intervention in Syria's civil war.
"If Damascus comes under attack, Tel Aviv will be targeted and a full-scale war against Syria will actually issue a licence for attacking Israel," Iran's Fars News Agency quoted a Syrian military official as saying. "If Syria is attacked, Israel will also be set on fire and such an attack will, in turn, engage Syria's neighbors."
"We face major uncertainties regardless of what we do."
But U.S. policy experts say it is unlikely that Assad's military forces have the capabilities to launch another large-scale attack at this point, given how committed their troops already are fighting the rebels within Syria. Any retaliation by Assad's military will largely be small-scale and symbolic, aimed at generating headlines and support rather than hurting U.S. allies or targets, according to Anthony Cordesman, an analyst at the Center for Strategic and International Studies.
"Syria can have a token form of escalation, although it's essentially committed almost all of the power it has (to the civil war)," Cordesman said. "If they did do something large-scale, their reprisal risk could outweigh their gains. In a world where every rocket is massive in terms of media reporting, they could do low level stuff to get a lot of propaganda gains, and do a lot of that without provoking response (from the U.S.)."
2. Iran Will Take Aim at Israel
Iranian leaders also issued strong rhetoric in recent days, warning the U.S. to stay out of the conflict in Syria and threatening to retaliate against Israel in response to any military meddling. One official was quoted in Iran's Fars news service saying that Iran would "flatten the place (Israel) that is tied to the U.S.'s national security."
But if Iran launched an attack on Israel, Cordesman said it is unlikely that the U.S. would come to its ally's defense.
"Iran could try to demonstrate its power by either using elements of the Al Quds Force or sponsoring a third party attack on anything from U.S. targets to Israeli targets to Jordanian targets," Cordesman said. "Israel will probably manage it own defense. We have strong reason not to get too involved at a time when we are working with so many Arab states," he said.
If Iran opts not to strike Israel or Jordan, it could still bolster its support for Assad, according to Byman.
"Iran and Russia might step up their response, sending more fighters, encouraging more fighters from Iraq and Lebanon, sending more arms, and using more diplomatic pressure," Byman said.
3. Radical Groups Could Retaliate
Islamic extremist groups and militant groups such as Hezbollah could also plan retaliations against U.S. targets or allies, according to experts.
"There is always the possibility that Hezbollah might act out," Cordesman said. "Islamist extremist action is a possibility."
"A lot of (the reaction) depends on the specifics of how visible this strike is," said Byman. "Iran's biggest client is Hezbollah, which has problems of its own and is already deeply involved (in Syria's civil war). Iran could encourage them to be more involved, but to what degree?"
But Mike O'Halloran, of the Brookings Institute, says he thinks it's unlikely that any major actors in the region will want to entice the U.S. into becoming more involved in Syria.
"It's not exactly clear why they would want to do anything more," O'Halloran said. "Why rouse a sleeping giant? The U.S. will still be, after this, a country unlikely to become a participant in the conflict - even arming the rebels will be something we handle with kid gloves - so why would anybody on Assad's side want to change that?"
"If Syria is attacked, Israel will also be set on fire and such an attack will, in turn, engage Syria's neighbors."
4. U.S. Accused of War Crimes
"The charges that we've faked the intelligence are already taking place," said Cordesman of the Obama administration's assertion that chemical weapons had unquestionably been used by Assad's forces on civilians.
One strategy that Syria could employ to retaliate against the U.S. is to accuse them of war crimes, Cordesman explained.
"The broader issue is what happens after the strike? (Syria) may focus on any collateral damage, real or false, to accuse the U.S. of war crimes, to go the U.N. with that," he said.
5. No Repercussions, U.S. Succeeds at Deterring Use of Chemical Weapons
Of all the potential repurcussions that could come from a strike, one U.S. expert is convinced that the biggest one will be success.
"The most likely, and it's always important to underscore that you can never count on the most likely, is it's a one-off," said O'Halloran. "It's very clear that President Obama has no more interest than that, and President Assad would be foolish to give Obama a reason or justification or necessity for doing more."
"I don't think President Obama is going to do any more than punish and deter any further chemical use, and to reestablish deterrents about weapons of mass destruction issues and behavior around the world," he said. "He will feel he's suceeded if there's not, in fact, a subsequent attack and Iran and North Korea take note."
Cordesman and Byman agreed that, if the U.S. is successful at striking Syria once, the region will be waiting to see what we do next in the broader context of the Syrian war.
"We face major uncertainties regardless of what we do," Cordesman concluded.