The Iran deal just passed a new threshold of Senate support, in a huge victory for Obama

On Tuesday morning, three undecided Democratic senators — Gary Peters of Michigan, Richard Blumenthal of Connecticut, and Ron Wyden of Oregon — announced their support of President Obama's nuclear deal with Iran.

That makes it 41 Democrats on record supporting the agreement — enough to sustain a filibuster that could block the GOP's planned resolution of disapproval from ever making it out of the Senate.

Last week, Obama had already reached the magic number of 34 supporters necessary to ensure the deal would survive Congress. That was all he needed to ensure that his promised veto of the Republican measure — which would have blocked the sanctions relief crucial to the agreement — would be sustained.

However, these new supporters — if they all vote to filibuster the deal — would make his veto unnecessary. This was a purely symbolic fight, simply to save the president from the embarrassment of Congress passing a resolution condemning his administration's foreign policy. But it's a fight it now appears Obama has won.

As the Washington Post's Greg Sargent points out, though, there is one lingering caveat: Just because senators support the deal, that doesn't necessarily mean they'll support a filibuster against the GOP's disapproval resolution. Theoretically, these senators could call for an up-or-down vote on the measure. It seems unlikely that they'd split such hairs in today's Congress — where 60 votes are necessary for essentially everything — but we'll see.

This looks like a massive defeat for the deal's opponents

Coming after nearly two months of intense debate and lobbying from both sides, these announcements are the best indication yet that the deal's opponents have failed in their effort to persuade undecided Democrats to break with the president and block the agreement.

Though every single Senate Republican is likely to oppose the deal, only four Democrats in the chamber have joined them so far: Sens. Chuck Schumer of New York, Bob Menendez of New Jersey, Ben Cardin of Maryland, and Joe Manchin of West Virginia. Just one more Senate Democrat, Maria Cantwell of Washington, remains undecided.

To block the sanctions relief, opponents needed to assemble a two-thirds majority in both the House and the Senate that could override a presidential veto. And that's impossible to reach without a lot of Democratic votes, as I wrote in July:

Deal opponents once hoped that the agreement would become politically toxic, leading to many Democratic defections. But that hasn't happened. Instead, the key swing votes — including some of the most conservative Democrats in the Senate, like Claire McCaskill of Missouri and Joe Donnelly of Indiana — have been won over by the administration.

Of course, the vote hasn't been taken yet. Theoretically, it is possible that some senators who have announced their support could change their minds. But that's unlikely to happen in the absence of some shocking or dramatic revelation that greatly changes the facts as these senators understand them.

The state of play in the House is tougher for outsiders to gauge, but opponents appear to be well short of the 44 Democratic opponents they need there — just 17 Democrats have said they'll vote to kill the deal, compared with 117 who are supporting it so far, according to the Hill. Again, the deal's opponents would need a veto-proof majority in both the Senate and the House to keep the sanctions in place.