Left unchanged were other rules that the out-of-power party could use to grind the chamber's work to an excruciating crawl. That ranges from requiring clerks to read voluminous bills and amendments to forcing repeated procedural votes.
"There are so many ways of slowing things down in the Senate," said Robert Dove, the Senate's former long-time parliamentarian.
Monday starts a two-week, year-end Senate session in which Majority Leader Harry Reid, D-Nev., hopes to finish work on a modest budget deal, a defense bill and other lingering items.
It will also be the first test of how Republicans respond to the Democratic changes.
Monday's meeting marks the chamber's first since irritable lawmakers left town Nov. 21 for their Thanksgiving break. Earlier that day, Democrats used their 55-45 edge to reshape how filibusters work, changing the number of votes needed to halt procedural delays against most nominations from 60 to a simple majority.
The move angered Republicans, whose mood and exact reaction will become clearer when they return to the Capitol.
But in a chamber whose arcane rules give any single senator the ability to throw the brakes on much of its work, partisan friction can hurt.
"The fact is it changes personal relationships with everybody on the other side," said Sen. Tom Coburn, R-Okla. "It has damaged the ability of us to move forward."
The Senate is vulnerable to delays because its rules technically require votes on almost anything it does. This includes agreeing to not read aloud an entire amendment, agreeing to begin considering nominations, even letting committees meet while the Senate is in session.
To save time, the Senate usually does such things by unanimous consent -- a quick voice vote to which no one objects. But angry senators can block fast action.
Democrats could make GOP delays as painful as possible, such as keeping the Senate in all night and on weekends.
"We're going to seek to achieve as much as we possibly can and hope Republicans will cooperate with us, instead of just using knee-jerk obstruction," said Adam Jentleson, spokesman for Reid.
Republicans are already using the rules to flex their muscle.
When the Senate recessed for Thanksgiving, it did not approve a batch of noncontroversial nominations and bills, which it usually does before such breaks. With 60 votes still required to end filibusters against legislation, GOP senators are blocking final passage of the defense bill until Reid allows votes on Republican amendments.
On Monday, the Senate will vote to confirm Patricia Millett to become a judge on the U.S. Court of Appeals for the District of Columbia Circuit.
Millett is a prominent private lawyer who worked in the solicitor general's office under Presidents Bill Clinton and George W. Bush. Republicans used the old 60-vote requirement for stopping filibusters to prevent a vote on her nomination in October, a blockade that helped prompt Democrats to force the changes.
Her nomination was viewed as key by both sides. The appeals court is disproportionately powerful because it rules on White House actions and federal agency rules. Her ascension will tip the balance of that circuit's judges to five appointed by Democratic presidents, four by Republicans.
Minutes after the Senate altered the filibuster last month, senators voted by simple majority -- and along party lines -- to end GOP delays against her. A roll call on final approval has been locked in, and Republicans can do nothing but vote against her.
Over the next two weeks, Reid plans to push five more major nominees through the Senate.
They include Janet Yellen to lead the Federal Reserve, Jeh Johnson to head the Department of Homeland Security and Rep. Mel Watt, D-N.C., to lead the Federal Housing Finance Agency. There are also two more Obama picks for the remaining vacancies on the D.C. court -- attorney Cornelia "Nina" Pillard and U.S. District Judge Robert Wilkins.
There is little doubt all five will be approved. But time-consuming GOP delays are possible, especially against Watt. Some Republicans say he is not qualified to run an agency that oversees federally backed home lenders Freddie Mac and Fannie Mae.
"Their objective was to guarantee success, not to make the Senate more efficient," said Donald Stewart, spokesman for Senate Minority Leader Mitch McConnell, R-Ky. "There's nothing they did that makes the Senate go any faster."
Under Senate rules, once a filibuster is defeated, senators can debate nominations for circuit court judges and Cabinet-level appointees for 30 hours before a vote on final confirmation. For a lesser post like Watt's, the maximum is eight hours.
"I'm sure he'll get eight hours of debate because the American people need to know he's not qualified to fill that position," said Coburn.
Democrats say Watt, a 21-year veteran of the House Financial Services Committee, is well suited for the job and say Republicans consider him too liberal.
Republicans can also force at least one procedural vote on each nominee before roll calls are taken to end filibusters and for final approval. Each requires only a simple majority for Democrats to prevail.
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