How fortunate Massachusetts is to have Bill Galvin!

After almost a half-century in politics, the 75-year-old secretary of state would like nothing better than to close his long career as an elected official and enjoy a comfortable and lucrative retirement. He has already served a record-setting eight consecutive terms in his current position as the Commonwealth’s chief elections officer and record keeper. Since Galvin’s tenure as secretary of state began in 1995, Beacon Hill has cycled through seven governors, five House speakers, and seven Senate presidents. Galvin has easily dispatched every challenger, cruising to reelection every four years.

After so many decades in public life, Galvin is amply entitled to let someone else take over the responsibilities of secretary of state. But this selfless warrior, knowing that there is no one else in Massachusetts who can defend the state’s interests properly, refuses to abandon his post.

“To leave a battlefield in the middle of a battle, it’s something I’m not going to do,” Galvin declared last month, announcing his campaign for a ninth term that would keep him in office through 2031.

That battle seems to never end. When he ran for reelection in 2018, Galvin told the Globe’s editorial board that it was probably the last time. Four years later, he was back on the ballot for another term — but he made it clear that it would be his last hurrah. “I am certainly done here with this job,” he assured my former colleague Scot Lehigh in 2022. Alas, circumstances are always conspiring to keep him at his post.

Galvin is hardly an exception. Indeed, he’s practically a role model. The inability to relinquish power is among the most reliable constants in American politics.

Senator Ed Markey, who turns 80 this year and is the oldest senator in Massachusetts history, is running for another six-year term. He has been in Congress for 50 years but has no intention of stepping aside. He too insists that to leave office would amount to a dereliction of duty. “I’m going to be on the Senate floor, fighting those fights and making those enemies,” he told a radio interviewer last week. “I’m going to be there insistently and persistently and consistently fighting every single day.”

When Virginia Democrat Mark Warner first ran for the Senate, he assured voters that he would serve for only two terms. “I don’t want to be a lifelong politician,” he explained. “My view of public service is something you do for part of your life, not all of your life.” That was then; now, taking a more indulgent view of lifelong politicians, Warner is running for a fourth term.

Republican Senator Tim Scott of South Carolina assured his state’s voters when he first entered the Senate that he strongly favored term limits and would impose one on himself — two full Senate terms and no more. He reaffirmed the pledge in 2019, repeating that he planned to run for reelection in 2022 and “that will be my last one.” But it won’t be his last one. On Wednesday, Scott let it be known that he intends to run for reelection in two years. When a reporter asked whether he had misspoken when he said his last campaign would be in 2022, he replied with a straight face: “Oh no, no. I meant 2028.”

Why are so many elected officials unable to let go? One possible answer is that too many politicians are egomaniacs convinced they are indispensable. But perhaps there is a more clinical explanation: Power is intoxicating.

Neuroscientists who study addiction make the case that at the chemical level, the brain reacts to the high that comes with political authority in much the same way it does to any other repeated source of pleasure. The dopamine reward system — the same circuitry activated by listening to music or drinking alcohol or falling in love or going viral on social media — triggers a rush in response to the status, adulation, and the exercise of power that politicians crave. Anna Lembke, a Stanford University psychiatrist and one of the country’s leading addiction specialists, argues in her 2021 book “Dopamine Nation” that the compulsion to keep chasing a dopamine reward has a neurological basis. It’s not merely a failure of character or willpower. The brain, relentlessly seeking to re-create the pleasure it has come to expect, is wired to generate cravings that can be difficult to override.

A senator who has spent decades at the center of power — fawned over by staff, deferred to by colleagues, sought out by supplicants, cheered by supporters — has been receiving an extraordinarily potent dopamine stimulus, year after year, for as long as he can remember. When that stimulus is threatened, the brain responds the way it usually does when faced with the prospect of losing a reward it was hooked on: with resistance, excuses, or anxiety.

This is definitely not an argument for sympathy. Politicians who can’t bear the thought of giving up the perquisites of office are not helpless victims any more than philanderers are excused by the thrill of the affair or shoplifters by the rush of pocketing something that isn’t theirs. They are adults making choices — choices that deprive their constituents of fresh representation, block younger and perhaps more able successors, and subordinate the public interest to their own psychological needs. The addict’s compulsion may be real, but it does not excuse the addict’s behavior.

But the science does help explain why so many officials refuse to let go and why their rationalizations are so consistent and so predictable. The crisis is always too grave to walk away from. The successor is never quite ready. The battle, as Galvin puts it, is never finished. It is the same story, election after election, decade after decade — because the craving is the same.

When King George learned that General Washington, following the American victory in the War of Independence, planned to relinquish his command, he marveled that any victor who could voluntarily let go of power like that must be “the greatest man in the world.” Washington then confirmed the judgment by doing it again — stepping down voluntarily after two terms as president.

Our own political class has drawn the opposite lesson. To Galvin, Markey, Warner, Scott, and their countless counterparts across the country, the truly great public servant is the one who heroically, selflessly, year after year and decade after decade, refuses to stop serving. How fortunate we are to have them.