This weekend’s announcement that Sen. Jeff Flake (R-AZ) won’t back the Iran nuclear deal robs the Obama administration for now of claiming the symbolic victory that the agreement has bipartisan support.
President Obama had hoped Flake, a member of the Senate Foreign Relations Committee, might be one of a few Republicans to endorse the deal. Obama needs the support of at least 34 senators to sustain a presidential veto if Congress approves legislation to block the nuclear bargain. Right now, a majority of Senate Republicans have already come out against the deal.
But that’s not Obama’s only problem. Sen. Charles Schumer (D-NY) has declared he’ll vote against the agreement and Sen. Robert Menendez (D-NJ) is expected to announce his opposition on Tuesday.
Related: Despite White House lobbying, Senator Flake opposes Iran nuclear deal
So far, 20 Senate Democrats have announced their support for the agreement. While about half of the Democratic caucus has yet to declare their position, there are a handful of undecided votes that could tip the balance.
Here are the Democrats whose support – or lack of it -- could set off a ripple effect through the chamber.
Sen. Ben Cardin (D-MD) The ranking member on the Foreign Relations panel, Cardin has been tight-lipped about his support for the Iran deal, indicating he won’t announce which way he will vote until Congress reconvenes in September.
Cardin has served as a bridge between the White House and Foreign Relations chair Bob Corker (R-TN), brokering the deal that produced the bill providing Congress with the chance to weigh in on the deal.
A Jewish lawmaker, Cardin has come under pressure from the deal’s critics to oppose it. The White House is also lobbying him heavily, recognizing his vote could influence several other undecided Democrats.
Joe Manchin (D-W.VA) The red-state Democrat has said he is leaning toward supporting the agreement. A major critic of U.S. military intervention in the Middle East, Manchin, a member of the Senate Armed Services Committee, has voiced concerns that walking away from the deal now could lead to more conflict in the region.
If Manchin does come out for the deal, it could provide political cover to other undecided Democrats who represent conservative states, like Sens. Joe Donnelly (D-IN) and Heidi Heitkamp (D-ND)
Claire McCaskill (D-MO) McCaskill has avoided multiple attempts by the media to pin down her position on the Iran nuclear deal, saying she continues to study the agreement. The Missouri lawmaker was among the first on Capitol Hill to back former Secretary of State Hillary Clinton, who has called on Congress to back the atomic accord.
Chris Coons (D-DE) Coons, another Foreign Relations Committee member, has emerged in recent years as an important, thoughtful voice on international policy. A close ally of the administration, losing his support would be a major embarrassment for the White House and hand the GOP a public relations win on par with when Schumer announced his opposition earlier this month.
Michael Bennet (D-CO) While Senate Democrats have the advantage of only defending 10 incumbent seats next year, compared with 24 for Republicans, Bennet is expected to face a tough race next year. Outside lobbying groups have already spent millions advocating for and against the deal and could redirect those funds after the divisive September to tear down the incumbent.
If his campaign determines that voting for the deal could hurt him back home in Colorado, it could serve as a signal to other incumbents, and challengers in blue-leaning states like New Hampshire that Democrats must win in order to have a shot at retaking the Senate majority, that the agreement is a political loser.
