As Jonathan Schwarz notes over at Mother Jones, though it has no legal significance, the letter threatens to increase the political costs of a unilateral attack on Iran. The fact that at least 30 members of the Senate are publicly stating that no attack can occur without their consent may weigh on the Bush administration, even if they believe they have the legal authority to attack anyway. As Schwarz says, in the end all wars are ultimately decided less by legality than they are by politics.
Here is the full text of the letter:
Dear President Bush:
We are writing to express serious concerns with the provocative statements and actions stemming from your administration with respect to possible U.S. military action in Iran. These comments are counterproductive and undermine efforts to resolve tensions with Iran through diplomacy.
We wish to emphasize that no congressional authority exists for unilateral military action against Iran. This includes the Senate vote on September 26, 2007 on an amendment to the FY 2008 National Defense Authorization Act. This amendment, expressing the sense of the Senate on Iran, and the recent designation of the Quds Force of the Iranian Revolutionary Guard as a Specially Designated Global Terrorist, should in no way be interpreted as a predicate for the use of military force in Iran.
We stand ready to work with your administration to address the challenges presented by Iran in a manner that safeguards our security interests and promotes a regional diplomatic solution, but we wish to emphasize that offensive military action should not be taken against Iran without the express consent of Congress.
Signed by: Akaka, Baucus, Boxer, Brown, Byrd, Cantwell, Carper, Casey, Clinton, Dodd, Dorgan, Durbin, Feinstein, Harkin, Johnson, Kerry, Klobuchar, Kohl, Leahy, McCaskill, Mikulski, Murray, Reed, Rockefeller, Sanders, Stabenow, Tester, Webb, Whitehouse, Wyden.
UPDATE: Sam Stein at the Huffington Post received responses from the offices of Senator Biden and Senator Obama as to why they did not add their names to the letter:
"Senator Obama admires Senator Webb and his sincere and tireless efforts on this issue. But it will take more than a letter to prevent this administration from using the language contained within the Kyl-Lieberman resolution to justify military action in Iran. This requires a legislative answer and Senator Obama intends to propose one."
"Sen. Biden voted against the amendment urging the designation of the Iranian Rev. Guard as a terrorist group. He strongly opposed it because he believed it could be used by this President to justify military action against Iran. He has also made clear many times his view that the President lacks the authority to use force against Iran absent authorization from Congress. He didn't need to clarify that position - he's been clear from the start," said Biden spokesperson Elizabeth Alexander.
Neither response seems all that convincing. While Obama's office is probably correct in saying it'll take more than a letter to counteract the Kyl-Lieberman resolution (which Obama neglected to vote on), it doesn't follow that signing a letter opposing an attack on Iran somehow precludes him from introducing binding legislation. As for Biden's claim that he didn't need to clarify his position -- why not? Certainly signing a letter clarifying it again couldn't hurt, could it?