Senate Republicans and Democrats are facing their own internal day of reckoning Tuesday, with each side poised to see a roster of new faces in key committee spots and the potential for a wholesale shakeup of the Democratic leadership.

Regardless of which party comes out on top, internal GOP Conference rules and the cornerstone South Dakota Senate race have the potential to set in motion the biggest shifts in Senate leadership in a decade.

A Republican victory, particularly any expansion in their current 51-49 edge, would solidify Majority Leader Bill Frist’s (R-Tenn.) political standing, both in the chamber and among conservative activists around the nation. A slew of new GOP chairmen would take over critical committee posts, including Appropriations and Judiciary.

And with an expanded Republican majority, GOP leaders would almost certainly seek a greater share of seats on committees — currently they have a one-vote edge on each — and a larger share of the panels’ budgets and staffs, meaning fewer key committee slots for Democratic Senators and fewer jobs for their aides.

A Democratic takeover of the chamber, on the other hand, would be a dramatic blow to Frist, who plans to step down at the end of 2006 and could be a potential contender for president in 2008. A Democratic victory Tuesday — up to nine races for seats in the chamber currently could go either way — would almost certainly mean Minority Leader Tom Daschle (D-S.D.) succeeded in beating back the challenge of former Rep. John Thune (R).

A newly re-elected Daschle next year would be the Republicans’ worst enemy, having survived a near-death experience only to come back more determined than ever to thwart President Bush’s agenda or aggressively push President John Kerry’s issues.

Daschle and his incoming chairmen, including Sens. Edward Kennedy (D-Mass.) and Patrick Leahy (D-Vt.), would be champing at the bit to get their first extended chance at leading the chamber, other than the 18 months they held power in 2001 and 2002 — almost all of which was dominated by concerns regarding the Sept. 11, 2001, attacks.

Interviews with top Senate aides, all of whom demanded anonymity, revealed a chamber at a potential tipping point where Tuesday’s results could reshape the roster of personalities who lead it for years to come. Aides were loath to speculate about potential losses on their side — although one GOP adviser didn’t hesitate to refer to “the inevitable Daschle defeat” — but the reverberations of potential setbacks are already resonating in the backs of the minds of Senators and aides.

The South Dakota Linchpin

The Senate Democratic Caucus has the most immediate concerns on Election Day, with the fate of its leader for the past decade hanging in the balance.

A Daschle victory would stiffen the spines of a Caucus that has been playing very strong defense against the Bush administration. In that outcome, the only big question mark in the leadership team would be choosing a new chairman of the Democratic Senatorial Campaign Committee to replace Sen. Jon Corzine, who is almost certain to run for governor of New Jersey unless offered a top position in a Kerry administration.

But a Daschle defeat would set off a chain reaction in the Caucus, ending the term of the fifth-longest serving Democratic leader in the chamber’s history and creating a series of potential leadership battles.

Minority Whip Harry Reid (Nev.) is clearly best positioned to take over for Daschle, having been a loyal deputy for the past six years. Reid, who may have once been considered a bit too centrist on social issues to lead a liberal Caucus, has earned chits as a pit bull on the floor.

He further endeared himself to the Caucus last month by turning over $1 million to the DSCC from his campaign account, an act that prompted several others to produce six-figure checks. Aides and strategists assume that, in the event of a Daschle loss, the best-case scenario for Reid would be a Kerry victory. That would mean the party’s message delivery would be run out of the White House and the less-than-telegenic Reid could devote himself to serving as Democrats’ procedural and legislative tactician.

Under this scenario, one lobbyist suggested Reid would be “anointed” leader without a challenge.

If Daschle loses, the only way Reid doesn’t take the glide-path to become leader would be if Tuesday results in widespread political bloodshed for Democrats: a Kerry loss, a Daschle defeat and a net loss of a couple Senate seats.

Some suggested that such a bloodletting would require some contemplation on the Democratic side about whether the Caucus could hold its leadership elections in mid-November as currently planned. The timing issue could also arise if there is a runoff in Louisiana, which wouldn’t be held until Dec. 4, and a lengthy recount in any of the chamber’s battleground races.

The only Democrat ever mentioned as a potential challenger to Reid is Sen. Chris Dodd (Conn.), who greatly stepped up his political activity this cycle by forming a political action committee that has dished out $288,000 to candidates. He’s given an additional $200,000 to the DSCC from his campaign account.

But Dodd has not given any indication that he would actually take the plunge, and, when Daschle almost stepped down as leader to run for president in January 2003, Reid was widely credited with having secured more than enough votes to beat back a Dodd challenge.

Even if Dodd doesn’t take on Reid, there will almost certainly be a race for Whip, most likely pitting Sens. Byron Dorgan (N.D.) against Dick Durbin (Ill.). Dorgan has more seniority and is a close ally of Daschle’s, and his camp claimed to have the momentum to win the Whip’s race in 2003 before Daschle reversed course and remained as Minority Leader.

But Dorgan angered some colleagues at the end of 2003 when he supported the Frist-backed Medicare overhaul, which some in the Caucus view as a litmus test of party loyalty. Durbin has been politically active, dishing out more than $320,000 to Senate and House candidates this cycle.

Durbin is clearly to the left of Dorgan, and if there is a strong desire to install an aggressive, liberal Whip — particularly if it serves as a counterbalance to the more subdued Reid as Minority Leader — Durbin may have the edge.

GOP Leadership Team Set

With the exception of National Republican Senatorial Committee Chairman George Allen (Va.), the current GOP leadership team is expected to remain intact for the 109th Congress. Even if Republicans were to lose the majority, it is highly unlikely any GOP leaders would be punished because such a scenario would probably dovetail with a Bush defeat.

“For the Senate [GOP] to do poorly, the president would have to do poorly,” said a Republican Senate aide.

Still, a senior GOP aide said many Senate Republicans are baffled that several races are “tighter than we thought they would be,” particularly contests in Kentucky, Oklahoma and South Carolina. But the aide said blame for these close races rests with individual candidates who have either run lackluster campaigns or caused unnecessary controversies that have distracted from their message. Still, the aide suggested that Allen would probably be the scapegoat in the short term and a Democratic victory Tuesday might hurt Frist if he runs for president in 2008.

And, following a defeat in 2004, the GOP race for NRSC chairman in the 2006 cycle would only heat up. It currently pits Sens. Norm Coleman (Minn.) against Elizabeth Dole (N.C.), and both have been hitting the stump for candidates and dishing out campaign cash. This week alone Dole has been to Pennsylvania, South Dakota, Oklahoma, Colorado and returns today to North Carolina, where she’ll campaign the remaining days with Rep. Richard Burr (R-N.C.).

Revolving Chairs

For Republicans, an exercise in musical chairs will occur in the 109th Congress as several committees will have new leaders regardless of the elections’ outcome.

Most notably, Sen. Arlen Specter (R-Pa.) is in line to take the helm of the Judiciary Committee, the controversial panel that vets the president’s picks for the federal bench including nominees to the Supreme Court. Specter will play a key role in the nomination hearings of the next Supreme Court justice, as the aging court begins to turn over.

In addition, Sen. Thad Cochran (Miss.) will be the new senior Republican on the powerful Appropriations Committee.

Because of a GOP Conference rule designed to prevent Republican Senators from heading any one committee for more than six years, Sen. Saxby Chambliss (Ga.) has a chance to head the Agriculture, Nutrition and Forestry Committee despite only having been elected in 2002.

If Sen. Pat Roberts (Kan.) remains as the top GOP Senator on the Intelligence Committee — the panel no longer has term limits and was elevated to “A” status — that opens up Chambliss’ opportunity at Agriculture. If Frist decides to appoint someone else to the Intelligence post, then Roberts could move over to head the Agriculture panel, relegating Chambliss to the second-ranking Republican slot on that committee.

Sen. Judd Gregg (N.H.) currently chairs the Health, Education, Labor and Pensions Committee but next month will have to choose between heading that panel or the Budget Committee. Should Gregg decide to stay at HELP, Sen. Wayne Allard (Colo.) would move up to the senior GOP position on Budget. But if the New Hampshire Republican decides to take the Budget reins, Sen. Mike Enzi (Wyo.) would then assume the senior Republican HELP post.

The Bayou Scenario

Most confusing of all for the chamber could be an Election Day that yields a 50-49 Senate, and a Dec. 4 runoff election in Louisiana if no candidate in that race is able to break the 50 percent threshold.

“We are not going to know anything until after Louisiana,” predicted a Senate Democratic aide, who asked not to be named. Should the election result in an evenly divided chamber, it is unlikely Democrats and Republicans would be able to reach an agreement similar to the one hatched in 2000 when the Senate was split down the middle, several Republicans and Democrats acknowledged.

“The well appears to be poisoned right now … and trust is in serious short supply,” said a senior Democratic aide, who spoke on the condition of anonymity. “This place is becoming so divided, I question if you can work out any type of agreement in this day and age.”