It's true, as some have pointed out in comments, that the Lieberman/Kyl resolution does not authorize war with Iran. In that respect, it is not analogous to the Iraq War Resolution. What it does do, however, is give Bush enormous cover if he ever decides to launch an attack on Iran. When he says, "My fellow Americans, last September, a bipartisan vote in the United States Senate designated the Iranian Revolutionary Guard a terrorist organization responsible for the deaths of hundreds of American soldiers. At 4am this morning, I asked the Joint Chiefs of Staff to prepare a bombing raid of their suspected safehouses and ammunition dumps..."
Democrats can complain and yell and scream, but their opposition will be terrifically compromised by having designated the Revolutionary Guard a terrorist group in the first place. What will the say: That they're a terrorist group killing American soldiers, but nonetheless, nothing should be done? It's ludicrous. And it eerily echoes the excuse many Democrats, like Hillary Clinton, give for their authorization of the Iraq War in 2002: They thought Bush would use the legislation to increase diplomatic pressure and intensify actions, not resort to military force. On this, Democrats were fooled -- or said they were fooled -- once. That more Democrats voted for the Iran resolution shows that they are decidedly willing to get fooled again.