But the conservative victories will alter the Senate, prompting incumbents from both parties to look warily to the next election.
Wealthy businessman Ron Johnson, a tea party-backed political novice, toppled Democratic Sen. Russell D. Feingold in Wisconsin and Republican Pat Toomey beat Democratic Rep. Joe Sestak in Pennsylvania.
Republicans also won President Obama's former Senate seat in Illinois after a closely fought battle between Democratic state Treasurer Alexi Giannoulias and Republican Rep. Mark Kirk.
Tea party candidates Rand Paul in Kentucky and Marco Rubio in Florida won Senate seats in those states, which were previously held by Republicans. Rubio beat both Democratic Rep. Kendrick Meek and Gov. Charlie Crist, the Republican who ran as an independent.
The GOP needed to pick up 10 seats to wrest majority control of the Senate from Democrats, but fell short. In the Republican upheaval of 1994, Republicans gained eight Senate seats.
The GOP lost one pickup opportunity in West Virginia as Democratic Gov. Joe Manchin III won the seat held by the late Sen. Robert C. Byrd for half a century.
Even though some of the long-shot tea party-backed candidates did not win Tuesday — Christine O'Donnell, for example, lost to Democrat Chris Coons in Delaware — the rightward jolt in the Senate will be apparent.
As voters registered their frustration, the Democrats' 59-seat majority shrank, likely leaving many Democratic senators nervous about advancing Obama's agenda as their own reelection battles come into view as early as 2012.
Similarly, moderate Republicans will be less likely to cooperate across party lines for fear of primary challenges from conservatives unwilling to compromise.
In the wake of Tuesday's unfolding power shift, the chamber that has been the scene of so many filibuster battles these last two years probably will see a less ambitious legislative agenda.
"These guys are going to be moving to the right," said Steven Smith, a political science professor and an expert on Congress at Washington University in St. Louis. "The question is, is that the right strategy for two years from now, four years from now? Or will it push the party too far to the right?"
Democrats may be forced to play more defense. As Republicans take over the House, the Senate represents Obama's last line of defense in the newly aligned Congress.
Republicans, however, face their own leadership challenges. Sen. Mitch McConnell of Kentucky, the party leader, must welcome outsider candidates, including some whom his party did not initially support.
Several GOP contenders, including Ken Buck, who is in a tight race in Colorado against Democratic Sen. Michael Bennet, found early backing instead from Sen. Jim DeMint (R-S.C.), the conservative kingmaker. They may be less beholden to the upper chamber's stately traditions.
GOP tensions also broke out in Alaska when Republican Sen. Lisa Murkowski launched a write-in campaign after losing her primary to tea party-backed attorney Joe Miller, creating a three-way race with Democrat Scott McAdams, the mayor of Sitka.
The GOP downplays the friction, pointing to the influx of seasoned elected officials, including Rob Portman, the former budget director during the George W. Bush administration, who won in Ohio; Rep. Roy Blunt, the House Republican who won a Senate seat in Missouri; and Dan Coats, the former senator who won his old job back in Indiana.