To force him to begin a withdrawal before then, the first step should be to rally the public by providing an honest and candid definition of what "supporting the troops" really means and pointing out who is and who is not supporting our troops at war. The next step should be a flat refusal to appropriate money for to be used in Iraq for anything but withdrawal operations with a clear deadline for completion.
The final step should be to put that president on notice that if ignores this legislative action and tries to extort Congress into providing funds by keeping U.S. forces in peril, impeachment proceeding will proceed in the House of Representatives. Such presidential behavior surely would constitute the "high crime" of squandering the lives of soldiers and Marines for his own personal interest.
Perhaps it is time to put it back on the table.