President Obama has put Senate Majority Leader Harry Reid in a bind.

Obama counts on the Senate’s top Democrat to help preserve the White House agenda on Capitol Hill. But on the issue of Iran, the president is facing a stampede of Democratic defiance, and Reid is the only one who can prevent an intraparty split.

Repeated veto threats from Obama have not curbed the appetite among a growing bipartisan swath of senators for a new Iran sanctions bill. Back in December, when the bill was only attracting the support of two dozen senators and had little chance of passing, Reid signaled he would bring the measure up for a vote.

Talks on an initial temporary nuclear deal between Iran and world powers, though, have made lawmakers even more skeptical of Tehran’s ability to negotiate in good faith.

Dozens of senators — including 16 Democrats — now support the new sanctions bill, drafted by Senate Foreign Relations Committee Chairman Bob Menendez, D-N.J., and Sen. Mark Kirk, R-Ill., bringing the total number of co-sponsors to 59.

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