No way can the rebel side in the Syrian civil war unseat the country's regime with the big power of Russia/Iran behind it.
The current monthly rate of about a hundred innocent Syrian civilians killed or wounded can be expected to continue without rebel surrender.
What quick action should the United States take? First, we can copy Israel and take no side in the civil war. We start by stopping all U.S. aid to the good side (rebel).
Then provide a leader for negotiating a peace treaty to free everyone in the country. I would suggest the greatest negotiator in the world, our President Barack Obama.