Washington (CNN) -- After three years of avoiding it, President Barack Obama finds himself being pushed toward military action in Syria.
Defense Secretary Chuck Hagel and Joint Chiefs Chairman Gen. Martin Dempsey both made clear that defeating Islamic State jihadists rampaging through northern Iraq would require going after them in neighboring Syria.
"Can they be defeated without addressing that part of their organization which resides in Syria? The answer is no," Dempsey told reporters Thursday. "That will have to be addressed on both sides of what is essentially at this point a non-existent border."
On Friday, Deputy National Security Adviser Ben Rhodes said the administration was looking at options beyond the current airstrikes in Iraq against the Sunni extremists known as ISIS.
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"If we see plotting against Americans, see a threat to the United States emanating from anywhere, we stand ready to take action against that threat," Rhodes told reporters. "... We're actively considering what's going to be necessary to deal with that threat, and we're not going to be restricted by borders."
Separately, U.S. officials told CNN there are longstanding and ongoing talks inside the military about increasing airstrikes in Iraq and even the possibility of tailored airstrikes inside Syria against specific ISIS targets.
But the officials stressed that no decisions have been made by the White House.
So a President who rejected calls by his advisers in 2011 and 2012 to arm rebels fighting the government of Syrian President Bashar al-Assad faces a policy change certain to embolden critics in both parties of his reticence back then.
"There's a pretty good possibility that we and/or some kind of multinational effort will engage in hitting ISIS targets inside Syria," Frederic Hof, an Atlantic Council senior fellow and Syria specialist, told CNN on Friday.
Legal barrier evaporated
He noted the Obama administration has acknowledged sending U.S. forces into Syria earlier this year in a failed attempt to free Foley. That established a precedent of acting in Syria to protect U.S. citizens and interests, superseding any legal considerations such as being asked by the host government to enter, argued Hof, who was Obama's former point man on Syria.
"The sort of legal barrier that prohibited doing something inside Syria now seems to have evaporated," he said.
Rhodes called the rescue attempt of Foley "entirely legal," saying "you don't need to be invited in if you're trying to rescue your people from imminent danger."
"I think any additional actions we'd take, we'd want to consult with Congress," he added.
Obama already escalated U.S. military involvement in Iraq to combat ISIS less than three years after ending a lengthy war there.
In June, he sent military advisers to work with Iraqi and Kurdish forces against the lightning ISIS sweep through the north. Earlier this month, the President authorized limited airstrikes on ISIS targets and additional advisers to Iraq to protect U.S. personnel and minority groups threatened by the Sunni extremists.
Hagel emphasized the ISIS threat on Thursday, calling it "beyond just a terrorist group."
"They marry ideology, a sophistication of strategic and tactical military prowess. They are tremendously well-funded," he told reporters. "Oh, this is beyond anything that we've seen. So we must prepare for everything. And the only way you do that is that you take a cold, steely, hard look at it and get ready."
He refused to rule out the possibility of airstrikes against ISIS targets in Syria.
At the same time, Hagel and Dempsey emphasized that defeating ISIS requires a broad-based approach that includes diplomacy to forge an international coalition and better governance in Iraq and Syria to build public opposition to the extremists.
"Political reform will make it harder for (ISIS) to exploit sectarian divisions," Hagel said. "The United States and the international community will increase support for Iraq in tandem with political progress."
Expanding the military campaign into Syria comes with significant risks for a President who has based his foreign policy on avoiding what he characterizes as reckless interventions of the past, particularly the Iraq War launched by his predecessor in 2003.
It would give critics fodder for arguing that Obama's decision to keep out of the Syrian conflict contributed to the ability of ISIS to grow into the threat it poses today.
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U.S. bombs exploding in Syria also would allow Islamic extremists to argue that America remains an imperialist bully despite Obama's efforts to change the perception.
Hof warned that the evolving situation could play into the strategy of al-Assad, who has long dismissed the uprising against his leadership as a fight against terrorists.
Until now, al-Assad has allowed ISIS to grow in Syria because it joins his government in fighting the anti-government forces.
However, ISIS fighters have taken over rebel-held territory and even some government-held areas, causing al-Assad to launch airstrikes against them in some places.
"This is basically two criminal gangs who often in effect collaborate but now have a difference over real money over who controls oil fields and the like," Hof said of the relationship between al-Assad and ISIS.
Wiping out the Syrian opposition would leave only ISIS and al-Assad, who would then position himself to the West as the lesser of two evils and an ally in fighting the jihadists, according to Hof.
"What he said from the beginning is that the only people who oppose me are terrorists and the West should support me because I'm fighting terrorists," Hof noted.
Obama also could face a liberal backlash at home for launching airstrikes in Syria.
His former secretary of state, Hillary Clinton, has distanced herself from him on Syria strategy during his first term as she prepares for a possible presidential run in 2016.
To deter criticism at home and abroad, the United States should build a coalition against ISIS that includes regional countries such as Turkey, Saudi Arabia, United Arab Emirates, Qatar and Jordan that can contribute air power -- much of it provided by America, Hof said.
"All agree at some level or another that ISIS presents a threat," he noted.
Domestically, ISIS "has gone a long way toward helping the President make the argument to the American people," Hof said.
At the same time, he added, Obama "needs to reassure people that this effort does not presage boots on the ground or some kind of repeat of the Iraq experience."
Rhodes called Obama "very deliberate toward the use of force," adding that "he doesn't rush toward military action."
"The American people also understand that there's some threats that have to be dealt with," he said. "We will take direct action against terrorists who threaten the United States."