Senate Democrats were caught off guard Thursday when Republicans launched a pre-emptive fight over a one-month unemployment insurance extension.

Majority Leader Harry Reid (D-Nev.) had just wrapped up a marathon 15-hour voting session on the health care reconciliation bill that stretched over two days, finishing his yearlong effort to complete action on President Barack Obama’s top legislative priority.

But as Democrats held a victory press conference in a room off the Senate floor, Minority Leader Mitch McConnell (R-Ky.) and Sen. Tom Coburn (R-Okla.) were busy making an end run around Democrats’ plans to pass the unemployment benefits extension without offsets.

As Reid left the press conference, Chief of Staff Gary Myrick approached him with the bad news.

“Reid left the Mansfield Room very happy … after the event, only to be intercepted by his chief of staff outside of the chamber. He grabbed his arm and said he was needed on the floor right away,” Reid spokesman Jim Manley said.

McConnell’s gambit set off hours of tense negotiations, and while he and Reid ultimately agreed to a paid-for, one-week extension, that deal was scuttled by House Democrats.