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Negotiations appear to have fallen apart, and the ceasefire between rebels and the Syrian regime has effectively collapsed.
The peace talks, which have taken place in Geneva, Switzerland, are "at best stalled and at worst already collapsed," Robert Ford, the former US ambassador to Syria from 2011 to 2014 and current fellow at the Middle East Institute, told Business Insider in an email.
And if the regime and opposition fail to reach a deal, Syria's terrorism problem is likely to fester and grow even worse.
"Our strategy ... is that Assad leaves, the structures of the government remain in place - but without Assad - and that the moderate opposition becomes part of the government and there is a government that can give the Syrian people what they deserve, which is a country that runs and a country that's moderate and a country that treats its people decently," Carter told the Senate Armed Services Committee.
"We're a long way from that now, but that's the vision for Syria," he continued.
Fred Hof, a former special adviser for transition in Syria under then-US Secretary of State Hillary Clinton, said the US is pursuing "a very risky strategy of incrementalism" in Syria.
"If we win the race against time with ISIS in Syria we'll be very fortunate," Hof told Business Insider in an email.
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Hof noted that US officials seem to acknowledge that "as long as Assad is in power somewhere in Syria, there is no prospect for a political solution that would produce a united front against ISIS."
But the US might be damaging its credibility in the peace process that aims to end a five-year civil war that has caused massive bloodshed, an international refugee crisis, and the rise of terrorist groups in the Middle East, Ford said.
"In the absence of US pressure on the Syrian government and Russians to abide by the cessation of hostilities fully [the US] becomes irrelevant to securing a peace deal for Syria," Ford said, citing airstrikes on a hospital in Aleppo as a recent act of impunity on behalf of Assad regime allies.
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"The US keeps saying it is 'concerned' about Syrian government and Russian actions, but beyond handwringing it has no real response," Ford said.
The regime and its allies don't seem willing to budge on the issue of Assad staying in power. The opposition insists on a political transition that would see Assad stepping down, and the US insists that Assad cannot be part of Syria's future.
"Assad and national reconciliation just don't mix," Hof said. "Assad's portfolio of war crimes and crimes against humanity makes him pure poison."
The US seems to hope that Russia, which is backing the Assad regime and carrying out airstrikes against rebels in Syria, will help plan a political transition.
The Russians "are the ones that have the most leverage over Assad right now," US Defense Secretary Ash Carter told the Senate Armed Services Committee last week. "It's very important that they do that because, as [Dunford] indicated, there's no resolution of the Syrian civil war until that occurs."