The Senate is losing its lions.

Jay Rockefeller’s retirement from the Senate, which the West Virginia Democrat announced Friday morning, is the latest in a series of departures — by death, defeat or choice — that has rapidly sapped the world’s greatest deliberative body of many of the personalities that dominated the institution, and American politics, for the better part of three decades.

Since the 2008 election, here is just a sampling of the senators who have gone: Ted Kennedy (D-Mass.), Ted Stevens (R-Alaska), Daniel Inouye (D-Hawaii), John Warner (R-Va.), Robert Byrd (D-W.Va.), Pete Domenici (R-N.M.), Arlen Specter (R-then-D-Pa.), Olympia Snowe (R-Maine), and, of course, Vice President Biden (D-Del.)

Virtually every major moment you can think of in the Senate over the past 50 years happened because of the men and women listed above. These are senators about whom books have been written and about whom many more will be written. They are people who will be remembered as prime movers in the chamber.

In their place are a huge number of newcomers who have replaced not only the lions, but also backbench members in recent elections. Since 2008, 40 — yes, 40 — new senators have been elected — 20 Democrats and 20 Republicans, a remarkable bit of symmetry.

Some have quickly made their marks. For Republicans, Sen. Rob Portman (Ohio) was on the short­list to be Mitt Romney’s vice presidential pick, while Sen. Marco Rubio (Fla.) is regarded as one of the front-runners for the 2016 GOP nomination. (Of course, that is using the Senate as a springboard rather than a destination in and of itself.) On the Democratic side, Sen. Michael Bennet (Colo.) has been entrusted with leading the party’s campaign arm in the 2014 election, while Sen. Joe Manchin (W.Va.) has emerged as a leading centrist voice in a chamber increasingly devoid of them.

Still, no one would dispute that the Senate is not filled with the sort of major figures that roamed its halls even a decade ago. The bigger question is why.

Some of the change is, of course, natural attrition. The Senate has never been a particularly youthful institution and death comes for us all — as it did for the likes of Kennedy, Byrd and Inouye in recent years. The last World War II veteran serving in the chamber is New Jersey Sen. Frank Lautenberg (D), 88.

But it’s also clear when looking at who has left, and why, that the Senate — and the process to get there — is fundamentally different than in decades past.

Take Sen. Dick Lugar (R-Ind.), a respected voice on foreign policy, who had comfortably won reelection for several decades. In 2012, however, he underestimated the seriousness of a challenge from his ideological right. Lugar lost the primary, while the man who beat him, state Treasurer Richard Mourdock, lost the general election to now-Sen. Joe Donnelly (D). (Two years earlier, Utah Sen. Bob Bennett (R) lost his own reelection bid in much the same manner.)

Or Snowe, who despite facing no serious opposition in 2012, decided not to seek reelection, citing the “atmosphere of polarization and ‘my way or the highway’ ideologies [that] has become pervasive in campaigns and in our governing institutions.”

To be clear, none of the examples cited above — with the possible exception of Snowe — are perfect cases against the Senate. Lugar never went home to Indiana, which badly hurt him. Bennett fell victim to a nominating process dominated by conservative activists.

But the totality of the departures — regardless of the reason — has clearly made the Senate a place of smaller statesmanship and decreased national sway than in years past. The loss of so many long-standing senators also has robbed the Senate of much of its institutional wisdom and sense of self. The intractability that has dominated Senate proceedings in recent years — and led to aggressive efforts to change filibuster rules — seems to be directly traceable to the fact that the Senate we once knew — and the men and women who populated it— are gone.

Of course, all lions were cubs once. And there are already signs that some of the newly elected senators are in it for the long haul. But it’s hard to dispute that the golden age of the Senate is passing — if it has not passed already.