More than four years after Congress authorized President Bush to invade Iraq, Senate Democrats have announced a new effort to try to take back that authority. Democratic leaders say they plan to unveil legislation that would repeal the 2002 resolution authorizing President Bush to go to war. The binding measure would call for a withdrawal of combat units by May of next year. But the resolution would also grant leeway to keep soldiers in Iraq to fight al-Qaeda forces and train Iraqi troops. Meanwhile, House Democrats have apparently dropped plans to link further war funding to the readiness of combat forces.