Dianne Feinstein (D-Calif.) is 87 years old. She has been a United States senator for the past 28 of those years, which is three years longer than the youngest member of the incoming House of Representatives has been alive. She is not, reportedly and apparently, what she used to be — and that is not a surprise.

Yet this octogenarian may be the least of our problems. While a politician’s physical frailty reveals one kind of aging, a party’s lack of imagination reveals another.

Jane Mayer in the New Yorker spotlights Feinstein’s dimming mind: The senator repeated a question word-for-word, inflection-for-inflection in a recent hearing; she sometimes forgets she has been briefed on a topic almost immediately after having been briefed; she thanked Sen. Lindsey O. Graham (R-S.C.) for his “fairness” after the Amy Coney Barrett Supreme Court nomination hearings with a hug, for heaven’s sake. Some aides, however, say reports of Feinstein’s cognitive decline have been exaggerated.

Feinstein’s best defense? Picking on the eldest woman in a chamber famous for elderly men amounts to a double standard. Strom Thurmond of South Carolina tottered around Capitol Hill until he turned 100, not totally compos mentis. Charles E. Grassley (R-Iowa) is 87 today, will be 95 at the end of the term he seems to intend to run for, and tweets things such as, “If u lost ur pet pidgin /it’s dead in front yard my Iowa farm” and “I’m at the Jefferson Iowa DairyQueen doing ‘you know what’ !!!.” Grassley is third in the line of succession for the presidency.

Obviously, the performance bar ought to be higher regardless of gender. But if bemoaning aging bodies and aging brains in both parties has its merits, it also misses much of what’s wrong with the Democratic Party in particular: old blood, plain and simple.

Feinstein is the apotheosis of a hazard that haunts progressives. They are supposed to represent the country’s future, including the young voters who show up at the polls to propel its members to power. They are supposed to make progress; it’s right there in the name. And yet as time ticks on and the institution turns into a gerontocracy, a feeling of backward motion takes hold.

Rep. Nancy Pelosi (D-Calif.) is still speaker at 80, Sen. Charles E. Schumer (D-N.Y.) is still minority leader at a tender 70, and there’s no sign that anyone is planning for a transition. Second in command in the House is Steny H. Hoyer (D-Md.). He’s 81, a year older than his boss. Schumer’s Senate deputy, Richard J. Durbin (D-Ill.) is 76.

Admittedly, President Trump embodies the case against inexperience. Yet how are the new kids on the block supposed to get the experience to qualify them for bigger gigs later on when the old kids on the block keep their ranks closed? If we need Pelosi’s seasoned hand to wrangle a tiny majority amid untold polarization, we also need to start seasoning fresher hands now so they can take over down the line.

A 78-year-old Joe Biden is going back to the West Wing, though there’s no “vice” before his title. He could convince the citizenry that his inauguration heralds more than a restoration — if he weren’t so busy dusting off Obama-era officials for a reprise.

Biden’s pick for secretary of agriculture was President Barack Obama’s secretary of agriculture. An Obama chief of staff will oversee the Department of Veterans Affairs. A noted Obama foreign policy hand will head the Biden domestic policy council. Other old hands are returning, or will soon, some of whom are longtime fixtures in a world whose leaders have shown little interest in rearranging the pecking order. Biden’s team of top advisers is so stuffed full of friends of the family that the only place to stick spring-chicken outsider Pete Buttigieg, 38, was at the Transportation Department, which shows you how sensitive the incoming administration is to the optics of the age imbalance — and how insensitive to the substance.

The issue with the has-beens who won’t step aside is that they have earned scars that can be limiting. Some are damaged by sins of the past (easy to do if you’ve worked at the CIA, cut a budget deal or run a populous city). Others just risk running plays that worked fine in days of yore, even though the here and now has utterly transformed the landscape.

When Feinstein embraced Graham this fall, some wondered whether she couldn’t comprehend the partisan catastrophe at hand well enough to condemn it. But such incomprehension doesn’t have to come from senility — it can result from sclerosis, too, a common malady among those who’ve been part of a system for long that they can’t fathom the possibility of change.

The Democratic Party, itself far more than 87 years old, has lost more than a step.

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