For 51 years of war and peace, Republicans and Democrats rallied around a bill to pay the troops, buy ships and aircraft and set military policy.

Last week, the Senate couldn’t even agree on votes.

Under pressure from President Barack Obama, Senate Majority Leader Harry Reid, D-Nev., was determined to avoid a vote on adding a new batch of tough penalties against Iran to the National Defense Authorization Act as negotiators held nuclear talks in Switzerland. A deal announced Sunday temporarily freezes Iran’s nuclear program.

Reid wasn’t keen on replaying a fight over the health care law, opening up contentious issues such as government spying or allowing probably the last bill out of Congress this year to become a magnet for other matters.

“Everyone has to understand this is not going to be an open amendment process,” Reid told his colleagues as he sought to limit amendments and wrap up the $625 billion defense measure after some three days of debate. He contends GOP delaying tactics have forced his hand.

A power grab, complained frustrated Republicans who demanded they be allowed to offer amendments and get votes on them — the norm for decades on a bill that represents half the nation’s discretionary budget.

The GOP repeatedly carps about Reid’s heavy-handed control, manifested by the rules change on filibusters. Republicans say the defense bill could have been done months ago but was put off until the last minute to spare Obama a few national security black eyes.

“Republicans are entitled to some amendments,” pleaded Sen. Jim Inhofe of Oklahoma, the top Republican on the Senate Armed Services Committee. He offered a whittled list of 25 GOP amendments from the list of 350 put forth by members of both parties.

It was a no go, the latest traditionally bipartisan bill to fall on the hard times of a fractious Congress. In the new normal of congressional inaction, toss the defense bill on the pile with the stalled farm bill, the missing immigration measure and the incomplete individual spending bills.

With just a few legislative days left in the year, the latest machinations leave in jeopardy a bill that authorizes money for personnel, war-fighting equipment and the conflict in Afghanistan. The Senate has to pass its bill and reconcile it with a version the House approved in June.

If the Senate cannot break the impasse when lawmakers return Dec. 9, troops still will get paid and fighter jets will continue to be built thanks to the separate, all-encompassing spending bill. But major policy changes might be lost, including several new measures to stem the epidemic of sexual assaults in the military.

Doing without an authorization bill for the first time in half a century also would represent the fall of one of last bastions of comity in Congress.

“I’m nowhere close to giving up on completing the defense authorization bill, even though we will only have days, not weeks, to complete it,” Sen. Carl Levin, chairman of the Armed Services Committee, said in a statement.

Head down and shoulders slumped, Levin looked disheartened by the proceedings on the Senate floor. Elected in 1978, the Michigan Democrats has had two stints as the committee’s chairman. He’s retiring after next year.

The dysfunction is “approaching an all-time low,” said Sen. John McCain, R-Ariz., who like Levin has participated in far more cordial, as well as more open, debates of the defense bill.

The impasse combined with the brouhaha over how Democrats unilaterally changed the Senate’s filibuster rules on Thursday left the Senate’s defense stalwarts pessimistic about the road ahead.

“There’s a lot of turmoil and I’d like to tell you that the 2014 elections will fix everything,” McCain said. “I’m not sure that’s the case. I think the problems go deeper than that.”