When Rep. Barney Frank (Mass.) settles into his seat Tuesday, he will be preparing for his 32nd State of the Union address since coming to Congress in 1981. Sen. Daniel Akaka (Hawaii) has been watching presidents speak to Congress from his perch serving in either the Senate or the House for 35 years.

President Barack Obama’s moment at the podium will mark the final State of the Union for these retiring Democratic Members.

With 25 House Members and Senators heading for the exits instead of seeking re-election or another office this fall, Congress is losing more than four centuries of institutional memory and service.

Frank is perhaps the most storied among this cycle’s crop of retiring lawmakers. But many of the others have played — and continue to play — roles less in the spotlight but still crucial.

“These are people who really know the institution. They are workhorses; they are not people who make the news all the time but are very important in terms of knowing how the place works,” said James Thurber, director of the Center for Congressional and Presidential Studies at American University.

Consider Sen. Jeff Bingaman, a Democrat heading home to New Mexico when he completes his fifth term. Bingaman is known for forging bipartisan compromise without pizazz. As chairman of the Energy and Natural Resources Committee, the Democrat is widely respected for his knowledge about land and water issues, and he exemplifies “the way the Senate used to work 30 years ago,” Thurber said.

“I wish there were more Senators like Jeff Bingaman,” said Jim Manley, a former aide to Senate Majority Leader Harry Reid (D-Nev.). “He spoke up only when he had something to say.”

Another key Senator who is exiting, Jon Kyl of Arizona, has been a driving force in bridging gaps between the chamber’s GOP leadership — of which he is a member as Minority Whip — and his fellow conservatives.

With other behind-the-scenes dealmakers leaving Congress, what might be left in their wake? Partisans fret that longtime lawmakers are getting out because Capitol Hill has become such a toxic workplace.

Frank has made no secret he was fed up with what he sees as Congressional dysfunction, even though he was once known for navigating even the most treacherous political waters to get things done.

“If it’s too polarizing for him, and if he can’t do that anymore, what does that say about Congress? That’s a pretty devastating assessment,” said Brendan Daly, a former aide to House Minority Leader Nancy Pelosi (D-Calif.) who now heads public affairs at Ogilvy Washington.

“It makes it more difficult to get things done during a period of time when we have extreme partisanship,” Thurber agreed, predicting the next Congress will be even more likely to “deadlock and grind to a halt on big issues.”

While this Congress could represent the height of partisan turmoil, it has been degrading for years, Manley said.

“The place has radically changed,” said Manley, who believes that as the makeup of the chamber shifts, the Senate becomes more combative, “much more like the House.”

“You can’t fault them for wanting to leave this place,” he said.

Both chambers are losing keepers of procedure.

On the House side, Frank is the guy Pelosi has always turned to for parliamentary questions and to win debates when process was key, Daly said.

“Barney was kind of a lifer, the guy you thought would always be around,” Daly said. “That’s a big loss right there.”

Rep. David Dreier, who saw his California district nearly dismantled during redistricting, fills that role for the Republicans. The Rules chairman, first elected in 1980, has been coy about his re-election plans. Should Dreier opt to retire, as many closely watching the process in California expect, his exit would leave a void for his party as pronounced as Frank’s departure does for Democrats.

Consider some of the others on the list of retiring lawmakers: Rep. Jerry Costello (D-Ill.) won’t seek a 13th term. Rep. Dale Kildee (D-Mich.) is leaving after his 18th term. Democratic Reps. John Olver (Mass.), Lynn Woolsey (Calif.) and Maurice Hinchey (N.Y.) have served 10 terms each.

Not included on the retiree list are Rep. Jane Harman, who resigned in February after serving six terms, or Rep. Jay Inslee, who is running for governor in Washington state. The Democrat is serving his eighth term.

Seventeen-term Rep. Jerry Lewis announced earlier this month that he will step aside instead of seeking re-election, but overall, far fewer Republicans have declared they plan to leave Congress this cycle.

The news of the retirement of Rep. Wally Herger (R-Calif.) came during winter recess, and a statement from Ways and Means Chairman Dave Camp (R-Mich.) offered a sense of the tribute Herger is likely to hear on the floor before his final days in the chamber.

“Looking beyond his tremendous legislative service and contributions as a long-serving Member of the Ways and Means Committee, Wally is a personal friend whose kindness, approachability and respect for his constituents and colleagues are emblematic of a true public servant,” Camp said in a statement honoring Herger, the senior Republican on the panel.

“There’s no doubt that it can be tough to lose Members who have valuable experience on key issues, especially issues like national security and intelligence, where the learning curve can be very steep,” said Kevin Smith, a spokesman for Speaker John Boehner (R-Ohio). Smith added that, on the positive side, newer Members are given a chance to step up, “show their credentials and seize a big opportunity” to shine.

And many of the staffers who have served alongside the retiring lawmakers will land in other offices, so that will help make the transition easier.

Senate Historian Don Ritchie noted that each Senator’s exit carries enormous weight given the nature of the body as a personality-driven institution. “Every Senator has a great deal of individual power and influence. Anytime anybody leaves and comes in, it changes the institution,” Ritchie told Roll Call.

He noted the nine Senate retirements so far this cycle isn’t quite the record of 13 retirements announced in 1996.

It won’t be known until November how many other longtime lawmakers might be shown the door thanks to unsuccessful re-election battles.

No matter what happens, the freshman class in 2013 almost certainly won’t top the 94 newcomers in the 112th Congress, the largest group of freshmen since 1946.