During three decades on Fairfax County’s Board of Supervisors, Sharon Bulova became known as perhaps the nicest elected official in Northern Virginia, barely raising her voice during painful budget debates or the acrimony over a 2013 police shooting that brought shame to her community of 1.1 million residents.

But behind the scenes, Bulova (D) harnessed the talents of an old-school political boss, holding a firm grip as board chair since 2009 and patiently laying the groundwork for her moderately liberal influence to remain intact after she retires at the end of the year.

When she first considered stepping down in 2015, Bulova decided Supervisor Jeff C. McKay (D-Lee) — like her, a pragmatist — should be her successor.

But McKay declined to run for her spot that year, citing the need to spend time with his two young children.

So Bulova spent the next four years grooming McKay for this year’s election — making him chairman on the important budget committee she’d overseen for 20 years and putting him out front on other pressing issues.

The Tammany Hall-like tap on the shoulder stirred resentment among Fairfax County’s growing liberal wing, with some critics grousing about the idea of an appointed successor. Others fault Bulova for favoring compromise over dramatic action, opting for caution over charging ahead during her years steering Virginia’s most-populous jurisdiction.

In a rebuke of sorts, McKay faced three primary opponents in the Democrats’ first intraparty fight for the chairman’s seat in at least 50 years. But he won handily and easily beat Republican Joseph Galdo in last month’s general election.

“I felt it was my responsibility to speak out about who I felt would be a good successor. . . . There’s nothing wrong with that,” Bulova, 72, said in an interview, referring to the fact that half the board will be new come January, and that the state legislature as well as neighboring Prince William and Loudoun counties all lurched leftward in the election.

McKay, she said, “has good judgment in looking at both sides of different issues, not finding himself far in the extreme one way or the other, and working with the community.”

Those attributes have defined a political career for Bulova that began in 1987. She was a shy aide to then-Supervisor Audrey Moore (D) and reluctantly agreed to run for her boss’s seat in what was then the Annandale District, while Moore sought the chairman’s spot.

Both women won, and Bulova went on to serve five terms in what became the Braddock District before she was elected board chairman in 2009.

Bulova — who calls both Moore and Rep. Gerald E. Connolly (D-Va.), another former board chair, her political mentors — has modeled herself as a leader who takes pains to weigh all sides of an issue before landing on a decision.

As board chair, she navigated Fairfax through the storm of the 2008 recession and was a key figure in the Metrorail Silver Line extension toward Dulles International Airport that has helped bring soaring office towers and apartment buildings to Tysons and Reston. Her legacy includes work in the early 1990s as a founding board member of the Virginia Railway Express commuter train service, which tied Washington to suburbs as far away as Spotsylvania.

“Sometimes, I think people think: ‘She’s so mild-mannered; we can just roll all over her,’ ” Bulova said of herself. But she’s been icy when needed.

Like last year, when Bulova barred Trump administration officials from speaking at a county meeting about law enforcement and immigration after it became clear that they planned to only focus on fears about gang violence.

From the audience, a top Immigration and Customs Enforcement official testily accused the county board of censorship. Bulova held her ground, replying tersely: “I’ve got the floor.”

She also clashed with then-Schools Superintendent Karen Garza, who in the aftermath of the recession repeatedly accused the county board of failing schoolchildren by not allocating enough funds to fix deteriorating buildings and keep teachers from fleeing to other jurisdictions.

Bulova leaned on then-School Board Chair Tammy Derenak ­Kaufax, suggesting that Garza be reined in to protect the county’s image as a home to top-performing public schools, an important consideration for large employers.

To her own colleagues, she was more direct, fuming, “ ‘Who the hell does this superintendent think she is?’ ” McKay recalled. “I can’t think of someone or something that’s made her more upset than that.”

Since Garza resigned in 2016 to lead an Ohio-based education nonprofit, the relationship between school and county officials has been more harmonious.

Some liberals in Fairfax argue that despite the strong Democratic majority under Bulova’s leadership, the wealthy county has fallen behind in key areas, such as battling the effects of climate change or adding affordable homes. They cite Bulova’s reluctance in 2014 to push through zoning changes she supported that would have allowed more studio apartments in the county, a measure that homeowner groups argued would lead to crowded roads and schools.

“The District of Columbia is currently spending $100 million on affordable housing. Right now, Fairfax County, which is twice as big, is talking about spending one fourth of that,” said state Sen. Scott A. Surovell (D-Fairfax).

John Farrell, a former county Democratic Party attorney who remains active in Fairfax politics, said Bulova “always wanted to have unanimity, which effectively gave the Republicans a veto. If you want everything done unanimously, you’re not going to accomplish a whole lot.”

A closed political loop has existed inside Fairfax County’s government for decades, Farrell said, making it hard to bring fresh perspectives to the board. “They pick their own people and, then, they tell the rest of us who we’re going to vote for,” he said. “It’s not an open process.”

Bulova’s supporters say she was right to back McKay — whose years of experience, they contend, have equipped him to steer a less experienced board through a more ambitious liberal agenda without resorting to excessive spending.

“Basically, that starts with trying to be fiscally responsible so we can ensure that the other things can happen,” said Supervisor John W. Foust (D-Dranesville).

McKay said he, like Bulova, will champion a balanced approach. “There is a distinction between advocacy and governance,” he said. “Sometimes you can’t always do everything you want to do in one year.”

Bulova has monitored such talk with nostalgia. Inside her office suite at the county government center recently, a collection of board photos taken over the years sat on a vacated assistant’s desk, near stacks of files Bulova was sorting through to determine what should go to the county’s historical archives.

A fat folder held notes from a community dialogue on public swimming pool repairs that Bulova arranged as the Braddock supervisor during the 2000s.

Such forums have been her favorite way of finding solutions to Fairfax’s problems. It helped in 2015, at the height of public outrage over how the county handled a police officer’s fatal shooting of John B. Geer while he stood unarmed at his doorstep in Springfield.

Geer’s family sued, and public trust in the local police withered amid the county’s refusal to share details about the shooting with even Fairfax’s frustrated prosecutor. Bulova calls those days the darkest of her career.

“We did everything we could have wrong,” she said.

To quell the anger, she launched a committee that included activists, police officials and law enforcement experts to hash out a host of police department reforms.

The effort resulted in the creation of a civilian oversight board charged with reviewing police abuse cases, an independent auditor who examines cases involving use of force, and a Diversion First program geared to steering mentally ill offenders toward counseling instead of jail. The county also agreed to be more transparent about critical police incidents.

“The silver lining . . . was major reforms I’m proudest of during my term as chairman,” Bulova said.

The past few weeks have been a celebration of those and other milestones, including at Bulova’s final board meeting, which featured video tributes for her and three other departing supervisors — Catherine M. Hudgins (D-Hunter Mill), Linda Q. Smyth (D-Providence) and John C. Cook (R-Braddock).

That 12-hour affair was a reminder of the potentially temperamental times ahead. A group of angry homeowners declared that plans to add softball lights at a local park would ruin their property values. More than 200 hooting gun rights activists demanded that the county declare itself a “Second Amendment sanctuary.”

Bulova stayed kind and soft-spoken as she moved through the agenda items until the end of the meeting. She then turned to ­McKay from her seat on the dais.

“Everybody knows I endorsed Jeff, and I wish him well,” Bulova said. “Jeff, I think we’re in for a beautiful future.”