I thought of this right after my last post yesterday evening - I'm betting Lieberman put the kibosh on Reid and Pelosi's efforts to attach benchmarks. No coincidence in my opinion that the Lieberman quote came out about the same time that the Dems caved on the bill. Joe's choice - pull the bill or you lose the Senate.
Unless Republicans start to peel off from the WH, what this means is that Congress will not be able to push a bill though without Joe's approval. The Senate has essentially turned Republican for purposes of the Iraq war.