WASHINGTON -- After pushing through one of the most significant rule changes in Senate history, Majority Leader Harry Reid struck a solemn tone: "This is not a time for celebration."
But behind closed doors in a room off the Senate floor, some of the newer Democratic senators couldn't help themselves, gathering for a quick party to congratulate one another. They were the ones largely responsible for pushing the veteran Nevada lawmaker to pull the trigger on ending filibusters against most presidential nominations.
The partisan revelers were part of a new breed of Democrats emerging in the Senate. Mostly elected after 2006, these relative newcomers have only known a Democratic-controlled Senate and have little experience with successful bipartisan cooperation, due largely to the tea party's grip on the Republican Party.
Now they are hoping to become a new power center in the party, nudging the old guard to adopt more aggressive tactics in pursuit of legislative goals and largely brushing aside Republican threats of retaliation and obstruction. They see the rules and traditions of the Senate as having stifled the will of the majority and stalled President Barack Obama's agenda.
"The Senate is a graveyard for good ideas," Sen. Tom Udall, D-N.M., who along with Sen. Jeff Merkley of Oregon led the filibuster reform effort and won over veteran colleagues in a body where seniority was once the most valuable currency.
This newer class of Democrats came to Washington, not unlike the tea party Republicans, with a strong commitment to their ideals and policy goals. But while the tea party rule in the House has been characterized by attempts to stifle the president's agenda, Democrats see their goal as helping to implement it.
Thursday's action to limit the use of filibusters -- seen as so drastic it was termed the "nuclear option" -- shows they are willing to carve out a different path to get there.
"There's a time to reach across the aisle and there's a time to hold the line," said Sen. Christopher S. Murphy, D-Conn., the body's youngest member at 40, who was elected in 2012. "And I think so far this year Democrats in the Senate have done a very good job of mixing across-the-aisle compromise with some heretofore unseen spine-stiffening."
The time has come for Democrats to take a harder stance against the tea party Republicans, he said.
"These folks have come to Washington to destroy government from within and will use any tool at their disposal," Murphy said. "To the extent that we have the ability to take tools away from the tea party, we should do it. And one of the tools was the filibuster. Another was the belief that Democrats would cave in the face of another shutdown or debt default."
For Murphy, the failure of the Senate gun control bill earlier this year was the final straw. He took on the issue of gun violence after the Newtown school shooting in his state in 2012. A bipartisan bill crafted by Sens. Joe Manchin III, D-W.Va., and Patrick J. Toomey, R-Pa., had 55 votes but failed to advance.
"I was a proponent of filibuster reform coming into the Senate, but I became a revolutionary on this issue when we lost the gun bill," Murphy said.
The group also includes Elizabeth Warren, elected last fall in Massachusetts. Her firebrand style and unabashed liberalism have energized the party's left wing.
The senators' influence has already been seen in other fights, most recently in the 16-day shutdown, when new Democrats lobbied party leaders to stand up to Republicans -- a tactic that seemed to shock many on the other side of the aisle, who were betting that Democrats would blink first.
Next on their agenda is extending the filibuster rule change from presidential appointments to legislation, which would enable the Senate to move on issues including gun control and climate change.
The changing Democratic tactics may reflect a generational shift occurring in the Senate. It's almost certain that by the start of the next Congress in 2015, more than half of the Democratic caucus will have been elected since 2008, when gridlock reached new heights. But nine of the new Senate Democrats are former Congress members, all of whom served at least part of their time under Republican majorities.
The shift among Democrats has at times confounded Republicans, particularly on the filibuster issue. Aides to Sen. Charles E. Grassley of Iowa, the third-longest-serving Republican, said they had felt that Reid's most recent moves telegraphing the nuclear option were a bluff.
Senate Minority Leader Mitch McConnell, R-Ky., on Thursday railed against the actions of "uninitiated newcomers in the Democratic caucus," reminding them they had never served in the minority in the Senate. Those who have a longer memory "should know better," he added.
Six-term Sen. Carl Levin of Michigan was the only Democrat to speak out against his party's move, citing the late institutionalist Sens. Edward M. Kennedy and Robert C. Byrd in arguing against tinkering with long-standing rules.
"Before we discard the uniqueness of this great institution, let us use the current rules and precedents of the Senate to end the abuse of the filibuster," said Levin, who will retire after next year.