With the retirement of Sen. Evan Bayh (Ind.), every Democratic presidential hopeful from 2008 will have exited the Senate by the time the 112th Congress convenes in January — and they’ll have taken an abundance of experience and star power with them.

Bayh joins a group of veteran Democratic and Republican Senators, many longtime elected officials, who are set to end their Congressional careers at the end of the term. All told, those departures — as well as the death last year of Sen. Edward Kennedy (D-Mass.) — will leave the chamber less 232 years of legislative know-how and Washington gravitas that has characterized Capitol Hill for a generation.

Given the political volatility of the election cycle, the Senate makeover could be even more extreme come Nov. 2. And while current and former Senate aides from both parties agree it will take time for junior Members to find their sea legs, they say the chamber will continue to drive Congress’ legislative agenda and that new crop of dynamos will rise.

“The diminished star power is easily overcome. Younger Members will in time become the new faces of the institution, and if anything it eliminates some distractions and unnecessary drama when there are fewer celebrity Senators,” a senior Democratic Senate aide said. “The more notable trend is just that the Senator is getting younger, and as that happens, the traditions and customs of the Senate that used to pave the way for bipartisanship are observed less and less.”

The exodus began in the aftermath of the 2008 elections and was a product of the Democrats’ overwhelming success that year. Barack Obama gave up his Illinois Senate seat to take the oath of office as president, with 36-year Senate veteran Joseph Biden (Del.), a presidential hopeful that year himself, following his new boss to become vice president.

President Obama recruited then-Sen. Hillary Rodham Clinton (N.Y.), his top rival in the Democratic presidential primary, to run the State Department. He also hired away then-Sen. Ken Salazar (Colo.) to lead Interior. A year later, another 2008 White House aspirant, Sen. Chris Dodd (Conn.), facing a serious climb to re-election, announced he would retire at the end of his term after 30 years.

Bayh, who abandoned plans to run for president in 2008 during the early stages of a campaign that never formally launched, announced his intention last week to leave the Senate next year, when his second term is up. Sen. Byron Dorgan (D-N.D.), who didn’t run for president, is retiring after 18 years. Additionally, four GOP Senators are calling it quits, while one Republican, Mel Martinez (Fla.), resigned his seat last summer.

Among those leaving are three former governors: Republican Sens. Judd Gregg (N.H.) after 18 years, Kit Bond (Mo.) after 24 years and George Voinovich (Ohio) after 12 years. Sen. Jim Bunning (R-Ky.), a former Major League Baseball pitcher and member of the Hall of Fame, also is giving up his seat after two terms.

One GOP lobbyist said the combination of Democratic and Republican retirements amount to a loss of “eons” of experience and include unique, irreplaceable characters that have left an indelible imprint on the Senate and American politics. But, this lobbyist said, the chamber was designed to absorb such losses, helped along in part by experienced staff who will remain.

“Senatorial Darwinism will take care of itself and new leaders will rise,” the lobbyist said. “There are first-term Members who will move up, and those in tiers of the current leadership who will also rise. The Senate is by design an institution that is meant for permanence through change.”

This isn’t the first time the Senate has faced a generational shift among Democrats.

In the landmark election of 1980 that ushered California Republican Ronald Reagan into the White House, five Democratic Senators who were also national figures of their time said goodbye. Among them were Frank Church (Idaho), Warren Magnuson (Wash.), George McGovern (S.D.), Herman Talmadge (Ga.) and Birch Bayh (Ind.), Sen. Evan Bayh’s father.

However, among the incoming Senators that year were Dodd and Sen. Arlen Specter (Pa.), who was a Republican until 2009, when he bolted to become a Democrat. Specter is among this year’s politically vulnerable class of longtime Members whose loss in the midterms could further diminish the amount of experience and collection of unique Senate characters.

But perhaps more glaring indicators of what Election Day 2010 could mean for the Senate are the predicaments of Majority Leader Harry Reid (D-Nev.) and the GOP’s 2008 presidential nominee and the senior Senator from Arizona, John McCain.

Reid’s re-election is in as much jeopardy as any incumbent Democrat’s running this cycle. McCain is facing his toughest test in years via a Republican primary challenge from former Rep. J.D. Hayworth, long a darling of conservatives. Hayworth lost his re-election bid to a Democrat in 2006.

One former Senate Democratic leadership aide said the potential loss of experience from Reid or McCain or both would be a significant blow to the chamber and its ability to tackle large, complex issues. The prospects of completing successful negotiations over contentious legislation could suffer as new Members go through a period of on-the-job training, although some argue the 111th Senate hasn’t proved able in that regard, either.

“I’m an experience-matters person. I’ve seen too many times where a senior Member knows how to keep people in the room and keep people negotiating using a combination of a style that appreciates the Senate and the way you get things done there,” said this individual, who now works downtown.

Additionally, many of the Democrats set to retire from the chamber this Congress “might be really liberal but wanted to negotiate,” another Democratic lobbyist and former Senate aide said. Kennedy, the chamber’s “liberal lion,” was viewed that way by many Republicans, among them conservative Sen. Orrin Hatch (Utah).

Should the Democrats suffer heavy losses this November — and particularly if Reid loses — the Senate could face greater paralysis as his replacement retrenches with a majority moved to the left by the loss of both moderates and retiring liberal negotiators. Senate Majority Whip Dick Durbin (D-Ill.) and Democratic Conference Vice Chairman Charles Schumer (N.Y.) are expected to vie for leader if Reid loses.

A second Republican lobbyist, one who works closely with Democratic and GOP Senators, said the Senate could be additionally polarized as both sides of the aisle look ahead to the 2012 presidential election and as Members weigh a Senate map that at least initially appears to favor Republicans. Should the GOP manage to regain the House but not the Senate, the gridlock could be magnified.

“In the end, the 112th Congress will likely end up more similar to the 110th, at least if the Democrats retain control of both houses, because they will have smaller numbers and would have to moderate their agenda after losses in 2010,” the GOP lobbyist said.