WASHINGTON – Senate Republicans on Thursday blocked the nomination of former GOP senator Chuck Hagel as the nation’s next defense secretary over unrelated questions about President Obama’s actions in the aftermath of the deadly raid on the U.S. diplomatic mission in Libya. Obama accused Republicans of playing politics with national security during wartime, and Democrats vowed to revive the nomination after Congress’ weeklong break.

By 58-40, with one abstention, the Senate fell short of the 60-vote threshold required to advance Hagel’s nomination to a final, up-or-down vote on his confirmation. Four Republicans voted with Democrats to end the debate and proceed to a final vote: Sens. Thad Cochran of Mississippi, Lisa Murkowski of Alaska, Susan Collins of Maine and Mike Johanns of Nebraska.

Obama reacted immediately, hammering Republicans for an unprecedented filibuster of a nominee for defense secretary and insisting that Hagel — a former two-term Republican senator from Nebraska and twice-wounded Vietnam combat veteran — will eventually win confirmation. He would succeed Defense Secretary Leon Panetta, who is stepping down after four years as CIA director and Pentagon chief.

“It’s just unfortunate that this kind of politics intrudes at a time when I’m still presiding over a war in Afghanistan and I need a secretary of defense who is coordinating with our allies to make sure that our troops are getting the kind of strategy and mission that they deserve,” the president said in an online chat sponsored by Google.

In the final minutes of the tally, Senate Majority Leader Harry Reid, D-Nev., switched his vote from “yes” to “no,” a procedural move that allows him to revive the nomination after the break. He set another vote for Feb. 26.

“Just when you thought things couldn’t get worse, it gets worse,” the Democratic leader lamented of the chamber’s bitter partisanship.

The successful Republican effort to block a vote on Hagel leaves one of the most contentious nominations of the Obama presidency in limbo, although Republicans signaled that they would relent and allow a simple majority vote on Hagel when they return from their recess.

Sen. Lamar Alexander, R-Tenn., voted against ending debate. But he said that he expects to change his vote, and he believes many of his GOP colleagues will do the same.

“I’m confident that after a reasonable period of time I’m going to vote to end the debate so that we can have an up-or-down vote on Chuck Hagel,” Alexander said. “I suspect there will be a large number of Republican senators who also do that.”