Marc Elrich, left, and David Blair, are neck and neck in the race for Montgomery County (Md.) executive. (From left: Sarah L. Voisin; Katherine Frey/The Washington Post)

MONTGOMERY COUNTY, with 1.1 million people, is Maryland’s largest locality, as well as the state’s economic dynamo — a place where leadership and governance are consequential. That’s why it’s faintly preposterous that as things stand now, the county’s top elected official is likely to take office on the strength of a primary last Tuesday in which the victor managed to collect votes from less than 6 percent of all active registered voters, or roughly 3.2 percent of Montgomery County’s total population. Not exactly a thundering mandate.

That state of affairs is a powerful argument for reforming voting systems in Montgomery and other localities, where only a plurality of votes cast — often in very crowded primary races — suffices for victory. Maryland’s legislature declined to embrace that reform for certain Montgomery County elections in this year’s session. Lawmakers who balked at doing so should now reassess.

That’s true no matter who prevails in the too-close-to-call Democratic primary for county executive. The nearly tied contenders are David Blair, a businessman, and Marc Elrich, a longtime County Council member. At the moment, Mr. Elrich leads by a few hundred votes out of the roughly 71,000 cast for the two of them, but several thousand absentee and provisional ballots remain to be counted; the winner will not be known until Thursday at the earliest.

The victor of the primary, which featured four other candidates in addition to Mr. Blair and Mr. Elrich, is extremely likely to win November’s general election race, given the county’s lopsided Democratic majority. (Just one potential wrinkle: an 11th-hour candidacy by a Democrat shedding her party affiliation to run as an independent, who would have until Monday evening to file a declaration of intent.) Whoever emerges, the winner’s authority would be undercut by having emerged from such an atomized primary.

Granted, primary elections in local races are relatively low-turnout affairs as a rule. (It’s worth noting that this year’s turnout was sharply higher than that in 2014.) Still, a better selection process is one we endorsed before the Montgomery County election took place: ranked-choice voting, which enables citizens to choose among candidates on a crowded ballot in their order of preference, resulting in an outcome where the victor is accorded an absolute majority. Candidates who finish last would be eliminated round by round, with their votes redistributed according to each voters’ ranked preferences until one candidate clears 50 percent of the ballots cast.

That procedure has been implemented, successfully, in San Francisco, Minneapolis and Santa Fe, N.M.; Maine recently adopted it for primary elections at the federal and state levels.

Is ranked-choice voting foolproof and guaranteed glitch-free? Probably not. It’s highly likely, however, to produce a winner with a better claim to legitimacy than having trounced all primary rivals — with backing from fewer than 6 percent of registered voters.