I have attempted a de-confusion in the comments, but since I'm not sure it will be noticed, I'm attempting a trackback.
Senator Liebermann offered an amendment to a Defence Spending Bill that calls Iran to task for supporting militia in Iraq that are killing members of the US Armed Forces.
The amendment as originally offered can be read as an implicit authorization to the President to use force against Iran.
However, contra RJ Eskow, Liebermann's language is not what the Senate passed 97-0 (and that is what has Digby confounded that the Democrats would hand the President a "loaded gun"). There were at least two crucial modifications to Liebermann's amendment before it passed. You can look it up in the Congressional Record (look for CR S9001-9002). Here is briefly what they are:-
First, this following clause was added to the end of the Lieberman amendment:
" (d) Nothing in this section shall be construed to authorize or otherwise speak to the use of Armed Forces against Iran."
Second, a clause was amended to read
" (1) the murder of members of the United States Armed Forces by a foreign government or its agents is an intolerable and unacceptable act against the United States by the foreign government in question; and"
(compare with the original Lieberman language
" (1) the murder of members of the United States Armed Forces by a foreign government or its agents is an intolerable and unacceptable act of hostility against the United States by the foreign government in question; and"
)----- The answer to Digby's confusion is that Liebermann's amendment was defanged and then passed unanimously.