When Majority Leader Harry Reid on Monday outlined the Senate agenda for the upcoming work period, he left out a bill that 59 members of his body are co-sponsoring: Iran sanctions legislation.

More than any single lawmaker, the Nevada Democrat has kept the sanctions bill at bay. By not scheduling it for the floor, he has averted a vote that very well might send the measure over to the House, where it would be assured of then being sent to the president’s desk.

Hill aides and analysts said Reid is motivated to keep the bill off the Senate floor by his allegiance to the White House; by progress in diplomatic negotiations to end Iran’s pursuit of a nuclear weapon that has dampened his caucus’s enthusiasm to enact new sanctions; and by his desire to avoid a reputation as someone who could be blamed for pushing the United States into another war.

President Barack Obama has identified the Iran nuclear program as his chief foreign policy concern.

By staving off the sanctions legislation that would be triggered by a failed final deal with Iran — and which Obama has threatened to veto — Reid has helped him pursue negotiations with Iran on the terms Obama prefers.

“The reason he’s holding off is because the White House is asking him to. The White House is putting a huge amount of effort into blocking this bill,” said Mark Dubowitz, executive director of the Foundation for the Defense of Democracies. The effort, Dubowitz said, has included daily calls from Secretary of State John Kerry, national security adviser Susan E. Rice and other top officials. “Obviously senators are under enormous pressure to not move the bill, including Reid.”

Dubowitz, who favors passage of a new round of sanctions to put pressure on Iran during negotiations, said the White House has launched a “withering assault” on bill backers, characterizing them as warmongers.

Some members of Reid’s caucus — even some co-sponsors of the bill — have asked not to be put in a position of having to override a veto on their president, fearing an even more withering assault, Dubowitz said.

A congressional aide who is following the process closely echoed some of Dubowitz’s arguments, but from a different perspective.

“I think he’s holding the line because in addition to the obvious answer that he’s carrying the administration’s water, I don’t think Harry Reid fancies himself a warmonger,” the aide said. “I think that he understands these negotiations are the best option we have for preventing a war with Iran and ending its nuclear program.”

The aide added that while pro-Israel and Jewish groups have been putting their own pressure on lawmakers, they aren’t as influential in Nevada as elsewhere.

“Las Vegas is not the west side of LA or New York or something like that,” the aide said. “Outside of those small communities that are very much gripped by this issue, most Americans want to see these negotiations succeed.”

Question of Timing

At the same time, said Robin Wright, a scholar at the Woodrow Wilson International Center, events such as the implementation agreement on the six-month deal reached between Iran, the United States and a group of other countries have slowed the Hill momentum overall.

“Timing is everything,” Wright said. “And the agreement in Geneva this month makes it harder for hardliners in both Washington and Tehran to push against diplomacy at the exact moment it’s beginning to look possible.”

That unhurried climate to act on a sanctions bill could change dramatically if Iran fails to implement the terms of the interim accord or if negotiations for a final agreement collapse. The American Israel Public Affairs Committee and Senate supporters seized on an interview that Iranian President Hassan Rouhani gave to CNN last week while attending the World Economic Forum in Davos, Switzerland.

In the interview, Rouhani was asked if Iran would destroy its centrifuges. “Not under any circumstances,” Rouhani replied.

Under the interim accord, Iran must halt its production of 20 percent enriched uranium and give up its stockpile of the enriched nuclear fuel. The accord does not require Iran to destroy centrifuges. In the negotiations for a final agreement, the United States and five major powers want Iran to reduce the number of its 19,000 centrifuges as a way to limit its nuclear enrichment program.

Nonetheless, bill backers want to put their stamp on the final agreement — the legislation includes a provision whereby Congress could pass a resolution of disapproval on the final deal and trigger the sanctions — and have cited Rouhani’s remarks as evidence that he’s not serious about important concessions.

“Rouhani has to worry about his hardliners at home, just like Reid does,” said Doug Bloomfield, AIPAC’s former legislative director and a frequent critic of the organization.

Bill Prospects

Though momentum has stalled for a Senate vote on the Iran sanctions bill, Bloomfield notes that AIPAC has positioned itself well as Obama pursues a final Iran nuclear accord.

“They’ve already got 59 co-sponsors,” he said. “The administration and Reid are on notice. That’s not chopped liver.”

While some observers see the momentum for the bill as having stalled, others contend that it will continue to build over time, owing to some national opinion polls that point to Obama’s position weakening and damaging remarks from Iranian officials.

Reid “is responsible for keeping the chamber Democratic in the fall and I think he knows that the longer he puts off a vote, the more politically untenable his position becomes,” said a senior Senate aide.

The stance by Rouhani “bolsters the case for this legislation as possibly the last best hope to pressure the Iranians to dismantle their nuclear program before military action becomes the only available option,” the aide said. “Clearly, without the threat of future sanctions, Iran will not dismantle its infrastructure, which means either Iran one day gets the bomb or targeted military strikes destroy Iran’s nuclear infrastructure first.”

Dubowitz also warned of the potential for Reid’s and the president’s position to backfire.

“The consequences for the White House of blocking the bill, and attacking senators as warmongers, are that the White House will own the failure if Iran refuses to reach an acceptable deal and ends up with the capacity for a nuclear weapons breakout,” Dubowitz said. “Reid, too, will be complicit in this failure if he is perceived as standing against the majority of his colleagues.”

Reid’s office did not answer a request for comment.

While Reid said in November he would advance a sanctions bill on the floor when lawmakers came back from the Thanksgiving break, that pledge coincided with an attempt to keep any Iran sanctions amendments off the fiscal 2014 defense authorization bill.

It also preceded the six-month agreement negotiators reached with Iran in November.

Reid backed off the pledge upon returning from the break. And on Jan. 14, he said of the negotiations that he wanted to “wait and see how this plays out.”

Jonathan Broder contributed to this report.