FAIRFAX COUNTY, among the nation’s best-educated, wealthiest and more diverse localities, has been well led by an array of long-tenured and moderate elected officials, most of them Democrats in recent years. Now, for the first time in decades, a vacancy for the chairmanship of the Board of Supervisors, the top job in a county of nearly 1.2 million people, has triggered a contested primary, on June 11, among four Democrats. The best by a mile is Jeff C. McKay, one of the region’s most knowledgeable, effective and experienced local leaders.

Mr. McKay would be an excellent successor to the even-keeled incumbent, Sharon Bulova, who took office just as the recession sapped Fairfax’s tax base, steered the county steadily through the storm and was instrumental in managing transportation upgrades and maintaining the county’s standing as a magnet for employers and jobs. It’s no surprise that the levelheaded Ms. Bulova is supporting Mr. McKay’s candidacy. In more than 11 years as the Lee district supervisor, he has been the board’s go-to authority on boosting funding for Metro, parsing the county’s $4.4 billion budget and managing state legislation with a bearing on Fairfax.

Tough-minded, measured and strategic, Mr. McKay is respected by his colleagues on the board, deeply popular with his Lee district constituents (whom he served for more than a decade as a staffer before running for office), and in touch with his counterparts around the region and the state.

His priorities — protecting and growing Fairfax’s affordable-housing stock; revitalizing older and poorer areas, including the Route 1 corridor; and deepening the county’s commitment to minority communities and sustainable environmental programs — are broadly similar to those of his primary opponents. What’s different is his track record and broad command of local and regional issues, which testify to his ability to get things done.

His three Democratic rivals do not share those attributes. They include Timothy M. Chapman, a wealthy developer who chaired the Virginia Housing Development Authority but has little experience at the local level beyond building housing; Ryan McElveen, a school board member who has antagonized supervisors he now seeks to lead; and Alicia Plerhoples, a Georgetown University law professor.

Ms. Plerhoples, who has impressive academic credentials, is new to local politics. That’s part of her appeal to activists energized by her candidacy; it’s also her Achilles’ heel. She is long on talking points but lightly informed on a range of issues, even ones she names as priorities, such as affordable housing. Ms. Plerhoples presents herself as a consensus builder, but the centerpiece of her program — raising $100 million annually by imposing a countywide meals tax — has been sharply rejected twice by Fairfax voters, most recently in 2016.

We have occasionally supported relatively inexperienced candidates for local office who have managed to master local issues and devise innovative ideas. In the Fairfax race, there is no such candidate. Mr. McKay possesses that mastery, along with sensible, progressive priorities and a proven knack for problem-solving.

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