In informing Congress Thursday that Syria’s government may have used chemical agents against the population, the Obama administration stated that “no option is off the table” should future evidence confirm the mounting suspicions.

The phrase, evoking America’s current confrontation with Iran and past ones with Iraq, prompts more questions than it offers clarity for how President Obama will navigate a worsening civil war that already has killed more than 70,000 people.

Would Obama send American forces to Syria if a United Nations investigation proves Syria’s President Bashar al-Assad has used the nerve agent Sarin in restive towns? And if he would not do so at a time when, in his words, “the tide of war is receding” after more than a dozen years of overseas conflict, would U.S. prestige suffer in the eyes of allies and antagonists alike?

The administration is already behind France, Britain and Israel in asserting that Assad most likely used chemical weapons against his people, and members of Congress from both parties were quick Thursday to seize on the acknowledgment as a “game changer” for U.S. policy. Even public opinion, according to recent polling, suggests that may be the case.

“The administration has confirmed that the Assad regime in Syria has crossed a dangerous, game-changing red line,” House Minority Leader Eric Cantor (R-Va.) said in a statement, which called on members to attend a classified briefing Friday morning.

The administration has made clear that it has monitored closely allegations of the Syrian government’s chemical weapons use since December, when reports first surfaced. But Obama has sought to downplay them as much as possible, given the consequences facing the administration if true.

On Thursday, Miguel Rodriguez, Obama’s chief liaison to Congress, made clear in a letter to the Hill that the administration will continue to seek a United Nations investigation to determine definitely whether chemical weapons have been used and to what extent.

Doing so buys the administration some time to decide a course of action, even as congressional Republicans raised concern about delays.

“Given our own history with intelligence assessments, including intelligence assessments related to weapons of mass destruction,” a senior administration official told reporters Thursday, “it’s very important that we are able to establish this with certainty.”

Obama is already facing the prospect of a military confrontation over Iran’s nuclear program after vowing that he would use all means necessary to prevent the Islamic Republic from developing a nuclear bomb – something the government there has denied pursuing.

Now he must weigh his potential action or inaction in Syria against his policy toward an Iranian government on the lookout for signs of faltering American resolve. A U.S. military action in Syria would open up a new front in the Islamic world, but it could also serve notice to Iran that Obama means what he says when he draws red lines.

There are also options short of direct intervention, likely far more appealing to the president.

After leaving Iraq and setting an end-date to American combat operations in Afghanistan, Obama wants little less than a new war in a Muslim country, particularly in the heart of the strategic Arab Middle East.

He intervened in Libya after securing Arab support, based largely on Col. Moammar Qaddafi’s threats to slaughter the people of Benghazi. But Obama did so in as low a profile way as possible, lending U.S. military aircraft, ship-to-shore missiles, and intelligence to a broad effort featuring European leaders as the face of the intervention.

Qaddafi was killed, as were four Americans, including Ambassador J. Christopher Stevens, the following year. Libya is still searching for stability.

Obama could begin rallying support for a similar international effort, led in the early stages by the United States. Such a move would remove the politically fraught decision to send U.S. ground forces into harm’s way, but assert, even at this late stage of Syria’s civil war, a potentially decisive American effort on behalf of the Syrian opposition.

That might be the farthest Obama chooses to go, if he even goes that far. What continues to complicate the administration’s policy in part is the nature of Syria’s armed opposition, specifically how much of it may be animated by radical Islamist doctrine and anti-American and Israeli fervor.

Those considerations have led Obama to move more cautiously than some American allies in the region, including Saudi Arabia and Qatar, which are supplying lethal aid to the rebels. Obama recently decided to double the amount of U.S. humanitarian aid to Syria. But he has stopped short so far of sending non-lethal battlefield support such as body armor, night-vision goggles, and armored vehicles, something the rebels want.

In its letter to Congress, the administration stated Thursday that “we do believe that any use of chemical weapons in Syria would very likely have originated with the Assad regime.” The assessment exonerates the rebels from Assad’s charges that, if such weapons are used, it would be the opposition using them. Assad still holds the key to the arsenal, as Rodriguez pointed out.

Short of building consensus for international intervention, Obama could act unilaterally in a limited capacity, such as using ship-fired missiles to destroy runways used by Syrian military aircraft against rebels and civilians alike. Humans rights groups have advocated such action in recent months given Obama’s unwillingness to implement a no-fly zone over Syria.

Finally, Obama could begin working through the Friends of Syria, which includes Arab states and Turkey, to provide U.S. military aid to the Free Syrian Army, as the coalition of rebel forces is called. Sen. John McCain, the Arizona Republican who on Thursday received one of the Rodriguez letters, has called on Obama to begin supplying such lethal aid for months.

The politics facing Obama at home regarding Syria appear to change when the use of chemical weapons comes into play.

A Washington Post-ABC poll conducted in December, when chemical weapons allegations first surfaced, found that nearly three-quarters of respondents said the U.S. military should not get involved in Syria’s civil war. Only 17 percent said it should.

But support for U.S. military intervention shot up to 63 percent if the Syrian government used chemical weapons against its own people. The poll also found wide support for creating a no-fly zone.

“I am deeply concerned with reports that further confirmation of use may be outsourced to the United Nations,” House Speaker John Boehner (R-Ohio) said in a statement. “If Assad sees any equivocation on the red line, it will embolden his regime.

“After two years of brutal conflict, it’s past time for the President to have a robust conversation with the Congress and the American people about how best to bring Assad’s tyranny to an end,” Boehner added.

Scott Clement, survey research analyst for Capitol Insight, the Post’s independent polling arm, contributed to this report.

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