In the slow, steady movement of most Senate Democrats toward support for the Iran deal, there were few surprises. Sen. Cory Booker (D-N.J.) was one of them. Elected in 2013, the senator had a long record of support for Israel, which some traced back to his relationship with a controversial sect of Judaism. He was a friend of Rabbi Shmuley Boteach, the celebrity theologian who authored both Kosher Sex and many jeremiads against the Iran deal. (Like many prominent opponents of the deal, Boteach scored a ticket to see Israeli Prime Minister Benjamin Netanyahu's address to Congress this year.) Sen. Robert Menendez (D-N.J.), Booker's senior senator, came out strongly against the deal.

That made Booker's "yes," explained in a lengthy essay on the Web site Medium, a coup for the deal's defenders. And a target for critics. Boteach condemned Booker's choice. While campaigning in New Hampshire this week, Gov. Chris Christie (R-N.J.) told a series of crowds that Booker's statement was an example of how Washington failed the country, and how parties retreated into silos.

"He talked about how it was a deeply disappointing deal, and it was deeply flawed, gives us awful choices, and that he's deeply disappointed in the president," said Christie. "Listen, everybody. If you want to understand the disease of Washington, D.C., that piece by Cory Booker is about as good a statement as you're going to see... politics matters more than what's right."

That wasn't quite what Booker wrote. He never called the deal disappointing. "I believe rejection of the deal would allow Iran to achieve an aim it has wanted all along," he wrote, "a significant unwinding of sanctions without the constraints on its nuclear program that this deal provides." The deal was "deeply flawed," and the "alternative was worse." The Twitter-happy senator spent a good portion of the days after the decision retweeting and attempting to soothe critics.

Booker's decision, which came after Sen. Barbara A. Mikulski's (D-Md.) decision to back the deal, was not in itself decisive. But it got the Democrats closer to a 40-vote bloc that could filibuster a resolution of disapproval.