When the US and Russia agreed to negotiate a process for a transitional government in Syria, the goal at the time was to have a transitional government in place by August 1. Secretary of State John Kerry today referenced that, warning August is fast approaching, and threatening a “very different track” from the US if President Assad didn’t surrender power by then.
Exactly what was meant to happen by August 1 in the US-Russia deal isn’t nearly that cut and dry, and the removal of Assad was never explicitly mentioned in the deal, or in the UN Security Council endorsement of the deal, a fact which led rebels to claim the US had sold them out.
After the deal was signed, however, the US began presenting the ouster of Assad as an obvious extension of the deal, though Russian officials had suggested that the plan all along was to get a unity government in place to prepare for free elections, which meant Syrian voters would decide who would be in power.
With peace talks so far failing to yield a transitional government of any sort, let alone one that the US supports, Kerry’s comments amount to a threat to try to impose regime change militarily if they don’t get their way soon.
Whether the US can actually do this or not remains to be seen, however, as the US has for all intents and purposes been trying to impose regime change in Syria throughout the civil war, throwing arms at various rebel factions throughout, and has accomplished very little.