Negotiations on how to introduce NDAA between Senators Reid and Collins failed, and Reid dropped the bill anyway in the same exact manner that he did in September.
Over the past week, Collins had made clear to Reid that in order to get enough Republicans on board to pass repeal (roughly 3 - 4), the amendment process needed to be fair, and it needed to be done after tax cuts were knocked out. Reid saw Republican resistance to NDAA as another partisan ploy, and while it was possible to get R's on board to see the issue through, the amount of time NDAA could potentially take up in the lame duck made pushing the issue much less appealing.
It's key to note here that Collins was not committing to a "no" vote OR ELSE. It's more that she was functioning as a mediator between noble Washington (Lieberman, Mark Udall, et al) and partisan Washington (Reid, McCain, et al). Her efforts convinced Reid Wednesday night to take more time to negotiate the process, negotiations that were not complete Thursday morning. Upon finding out the Republicans were ready to tackle tax-cuts yesterday morning, Reid chose to delay his decision on when to go forward on NDAA.
Thursday afternoon - while Sen. Lincoln was away on a dentist appointment and Collins out of the room - Reid unexpectedly and with little announcement dropped NDAA for a vote with a partisan speech mostly complaining about Republican obstructionism and how there wasn't enough time to do NDAA if they waited beyond Thursday to drop the bill (which was true only if Reid kept to the December 17th adjournment date he himself set). Collins rushed into the room in a last attempt to keep the bill from failing, pleading that she did not understand why he was doing this when negotiations were almost complete. Reid dropped the bill anyway.
Vote count and breakdown of the standlone bill, after the jump.