[More votes for. Significantly, on Tuesday Democratic Senators Tim Kaine of Virginia, Bill Nelson of Florida, and Barbara Boxer of California signed on. On the WaPo’s site, Greg Sargent explains why these are bellwether declarations.]

3. A potential vote against. I take this headline from Politico as a good sign for the deal’s prospects in Congress:

How can a powerful Democrat’s opposition be a good sign? Because it suggests that Schumer has already calculated that the administration can do without his vote.

For rococo parliamentary reasons, the crucial voting showdown is still several legislative rounds into the future. First the Congress would have to pass a measure condemning the deal, which Republican majorities in both the House and Senate will certainly do. Then President Obama would have to veto the measure, which he will certainly do. Then the Congress would have to override the veto, which requires a two-thirds majority in both chambers—and this is what the Democrats, even in their diminished numbers, should still be able to block with some votes to spare.

Schumer doesn’t put it this way, but obviously he is hoping that one of those spare votes will be his. His life will be easier in many ways—in minimizing hassle during his upcoming reelection run in New York, and thus maximizing his efforts to help other Democratic candidates so that he has a chance of becoming Senate majority rather than minority leader—if he doesn’t have to spend time explaining away a vote for the deal to his conservative and AIPAC-aligned constituents. If the deal goes through despite Schumer’s opposition, people who support the deal won’t care, and those who oppose it can blame evil Barack rather than valiant Chuck.

But what if it came down to a single vote, so that Chuck Schumer himself would determine whether a Democratic president’s most important diplomatic effort succeeded or failed? Call me a cockeyed idealist, but in those circumstances I just can’t believe he would join Senators Cotton, Cruz, Inhofe, et al. in voting “no.” Thus any “Schumer-no” signal now may indicate his confidence that enough other people are going to vote “yes.”

4. Reality. The UN Security Council has already approved the deal, and by a 15-0 unanimous vote—hardly its norm on controversial issues. So has the European Union. Sample report, from Reuters: “‘It is a balanced deal that means Iran won’t get an atomic bomb,’ said French Foreign Minister Laurent Fabius. ‘It is a major political deal.’” The Russians and Chinese are moving ahead as if the deal is done, because from the world’s perspective it is.

The remaining forceful public opposition is from the unified GOP plus some Democrats, and the Netanyahu administration plus other Israeli figures. Even if they prevail, they cannot stop the deal and make five other countries reinstitute sanctions. Although you’d hardly know it from the U.S. debate, the opponents’ writ does not run to China, Russia, Europe, or Iran. All that a congressional “rejection” can do is ensure that the safeguards negotiated in the bill never take effect. As Graham Allison put it:

If the U.S. Congress rejects this agreement and proposes sending Secretary of State John Kerry back to the negotiating table, Kerry will most likely find no one else there. Partners who have negotiated and compromised over 20 months to achieve this accord will conclude that the U.S. government is incapable of making agreements. The international coalition will splinter and the sanctions regime will collapse, with Russia and China leading the way, but with France and Germany not far behind.

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