The Iran deal's Senate math is looking good for Obama (so far)

Democratic Sens. Chuck Schumer and Bob Menendez's recently announced opposition to Obama's nuclear agreement with Iran suggested to some that the deal is in deep trouble in Congress.

But a flurry of new endorsements — the latest being from Sen. Claire McCaskill of Missouri on Thursday — are bringing Obama closer and closer to the votes he needs.

Earlier this week, Indiana Sen. Joe Donnelly also came out in favor of the deal. He and McCaskill are the second- and third-most conservative Democrats in the chamber, according to one political science metric. In a statement, Donnelly said a nuclear-armed Iran "would pose an unacceptable threat," but seemed to endorse the administration's argument that the only real alternative to this deal is war.

According to this excellent, regularly updated whip count by Amber Phillips of the Washington Post, 26 Senate Democrats have endorsed the deal so far. Based on public statements, Phillips characterizes five more Democrats as leaning yes, and 12 more as purely undecided. Schumer and Menendez are the only two publicly opposing the deal so far, though one more (Ron Wyden of Oregon) seems to be leaning no.

For any normal vote, those numbers would look quite bad for President Obama. But the math here is on his side — and is quite punishing for the deal's opponents. If opponents want to block the sanctions relief that's crucial to the agreement, they need to assemble a two-thirds majority in both the House and the Senate that can overcome a promised presidential veto. And that's impossible to reach without a lot of Democratic votes, as I wrote in July:

Javier Zarracina/Vox

Another way to look at the Senate math is that President Obama needs 34 Democrats on his side to ensure that his veto is sustained. And if we count the Post's five "lean yes" Democrats with the 26 outright supporters, that means he's only three votes short of getting the number he needs — and there are 12 more purely undecided Democrats (plus the "lean no" Wyden) that he can get those three votes from. That's a lot of options.

On the other hand, if the Post has characterized the leaners accurately, the deal's opponents would need to convince a vast majority of the still-undecided Senate Democrats to defy the president — a heavy lift. Indeed, Politico's Burgess Everett reports that it's not clear deal opponents will even get the 60 votes they need to pass a disapproval resolution through the Senate in the first place. (They'd need four more Democrats to get there.)

Beyond that, deal opponents would also need two-thirds support in the House of Representatives for a veto override. That chamber's large membership makes it tougher for outsiders to count votes, but 44 Democrats would have to side with every Republican to sustain a veto. According to a whip count by the Hill, 12 have publicly opposed the deal so far, though many are still undecided.

Nothing's certain until the votes are actually cast, of course. It's not utterly inconceivable that the Democrats leaning yes could change their minds, or that the remaining undecideds could all swing one way. But so far, it looks like the deal's opponents are still very far away from the numbers they need.

This article was updated with Markey and McCaskill's endorsements of the deal.

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