An interim deal with Iran on its nuclear program is complicating the future for the annual defense authorization bill, as Senate Majority Leader Harry Reid, D-Nev., must manage three clashing factions: senators intent on passing a new round of sanctions, a White House that opposes them and armed services negotiators who simply want to see their bill passed.

Republicans hellbent on attaching Iran sanctions to the pending defense authorization bill froze Senate action before Thanksgiving, and the Senate is scheduled for only one more week of work before Christmas. The Iran agreement has only brought more voices into the fold, with Democrats such as Sen. Charles E. Schumer of New York and Senate Foreign Relations Chairman Robert Menendez of New Jersey, calling for new sanctions legislation.

The tension between imposing stricter sanctions and approving the National Defense Authorization Act manifested itself in Reid’s own shifting statements. Last week, Reid vowed to push forward with a new sanctions bill after Thanksgiving, a move clearly designed to appease GOP members who refused to consent to amendments to the defense authorization bill without a promise on Iran first. But by Monday, the majority leader walked back his position, telling NPR that he would proceed with an Iran bill only “if we do need stronger sanctions.”

Armed Service Chairman Carl Levin, D-Mich., the manager of the defense authorization bill, said Reid’s previous, new-found commitment to an Iran sanctions measure was an effort to finish the bill while avoiding Iran amendments.

“I think he did what he needed to do today in order to avoid this issue interfering with the negotiations,” Levin said Nov. 21.

Sen. John McCain of Arizona, the former top Republican on the armed services panel, said that Iran sanctions and Reid’s then-vow to proceed on a bill had “no effect” on the larger defense authorization debate. But Sen. Lindsey Graham, R-S.C., one of the most outspoken advocates for stronger sanctions, said differently.

Graham is part of a contingent of GOP senators who are insisting on addressing the Iran issue. He said last week that he believed Reid’s promise to move forward was a good first step toward finding agreement, but warned that he and his allies would need another must-pass vehicle for an Iran bill if Reid removes the issue entirely from the defense bill.

“The Iran sanctions amendment they probably wanted to avoid. I think that’s probably why we couldn’t get a commitment on [proceeding]. If we could get an Iran sanctions legislation outside of the defense bill, that might give us a second chance at it,” Graham said. “[But] I want it to move on something that will get signed into law. I don’t know what vehicle, but I will be looking for a must-do vehicle.”

But as he announced the deal, Obama on Saturday night warned Congress against new sanctions, saying they could derail the talks and fracture the international coalition needed to enforce the sanctions in the first place. Secretary of State John Kerry made similar remarks from Geneva and said he had confidence in his former colleagues.

There are still more than 400 amendments pending to the underlying legislation. Levin said he had received unanimous agreement on 30 or so amendments to the bill but could not get a unanimous consent agreement on the floor to append them to the bill.

The chairman said he planned to do “a lot” of work on the amendment front to try to piece together a package that could get swift approval if Republicans choose to lift their objections. Last week, in frustration, Reid held a cloture vote on the bill itself in a last-ditch effort to wrap it up before Thanksgiving. Sen. James M. Inhofe, R-Okla., also exasperated by the Senate’s inability to make progress on the bill, had urged GOP colleagues to whittle down their amendment offerings or he would vote to close out debate.

“We’re a long way from giving up,” Levin said.

Levin and McCain talked on Nov. 21 about how detrimental failure to pass a bill would be for military families — and for both parties.

When asked how he might convince colleagues to cooperate, McCain said that veteran senators “know how to do” the defense authorization and that senators eventually would get on board with a bill that has passed every year for more than a half century.

“You convince them by saying, ‘OK. Here’s what we can do. Here’s what we can’t do.’ I’ve done it for years. It’s not rocket science. It’s hard. It’s harder this year because [Reid] only gives us a week, and it usually takes at least two weeks,” McCain said. “But it can be done because of the importance of the legislation. People don’t want to go home and say, ‘Your son’s not getting a pay raise this year because Congress refused to act.'”

There’s another trump card leaders might have in their hand if the situation gets dire. If Congress doesn’t pass an authorization, it would empower appropriators to make those decisions for them. If GOP senators don’t agree to proceed on the bill or approve it, that would leave No. 2 Democrat Richard J. Durbin of Illinois, the chairman of the Defense Appropriations Subcommittee, as the ultimate decider of how to deal with military spending.

Asked in late October about the possibility that he would gain more power if the defense authorization doesn’t happen, Durbin joked, “Wouldn’t that be nice? I’d like that.”

The Illinois Democrat added, “Well, you know, they’re given their chance.”