Marc Elrich in Rockville in October 2017. (Sarah L. Voisin/The Washington Post)

MARC ELRICH, the most insistently anti-business and anti-development member of the Montgomery County Council for more than a decade , has eked out the narrowest of victories in last month’s Democratic primary for county executive. Pending a possible recount — and notwithstanding a still-uncertain independent candidacy in November’s general election by another veteran council member, Nancy Floreen — Mr. Elrich now looks like the odds-on favorite to assume the top elected position in the heavily Democratic locality of about 1.1 million people.

To his credit, Mr. Elrich — whose 80-vote margin of victory amounts to a tiny fraction of the almost 130,000 primary votes cast and an infinitesimal share of the county’s 644,000 registered voters — has been saying conciliatory things. He has pushed back against the long-standing view that he reflexively opposes growth, correctly noting that his social agenda, which includes closing the racial achievement gap in public schools and expanding early-childhood education, is moribund unless Montgomery, whose commercial growth has stagnated for years, manages to attract new businesses and jobs. “If you’re trying to achieve what I want to achieve, then you need to have money,” he told The Post.

That assurance is welcome, as were his earlier ones that he would embrace a decision by Amazon to locate its second corporate headquarters in the county. (The company — whose founder and chief executive, Jeffrey P. Bezos, also owns The Post — has shortlisted Montgomery as a finalist for the project.)

Nonetheless, there are legitimate concerns about the prospect of Mr. Elrich leading Montgomery, which is why we opposed him. Those concerns were reflected in the fact that none of his past or present council colleagues endorsed him in the primary — though two have now done so for the general election. The fact is, Mr. Elrich until now has been an outlier who proudly positioned himself on the ideological extreme left, even in the context of a decidedly liberal county. Business and development leaders, whose confidence Mr. Elrich will need if he is to inject a dose of economic vitality into the county, are openly worried.

And with good reason. By tilting against sound land-use plans, Mr. Elrich played to anti-growth homeowner groups and repeatedly wound up on the short end of 8-to-1 votes on the council. By courting Venezuela’s help in funding local social programs, he embarrassed the county and proved himself a willing propaganda tool of one of the hemisphere’s most antidemocratic regimes. And by opposing a deal to bring the Fillmore music hall to Silver Spring — he said the county could get a better deal — he cemented his reputation for allowing the perfect to be the enemy of the good.

Mr. Elrich possesses an agile mind and a silver tongue; he is always ready with a plausible justification for his stands. The common thread, though, has been his resistance to reasonable compromise and a willingness to take potshots rather than half a loaf. If he does become county executive, he will need to calibrate those instincts.