VA 48th House of Delegates hopefuls David M. Foster (r), left, and Richard "Rip" Sullivan (d). (Foster and Sullivan/courtesy Foster for Delegate and Sullivan for Delegate)

IT’S HARD to think of an election date less likely to attract voters than a Tuesday in mid-August, which is prime vacation season. That may explain why William J. Howell (Stafford), the Republican speaker of Virginia’s House of Delegates, chose Aug. 19 for special elections to fill vacant House seats in two heavily Democratic districts. If enough Democrats are at the beach, the speaker seems to have reckoned, Republicans might have a shot.

One of those two seats is Northern Virginia’s 48th District, which hems the Potomac River from Crystal City to northern Arlington, then juts west into McLean. The district, entirely inside the Beltway, has been represented for 17 years by Del. Robert H. Brink, a Democrat who resigned in June to take a state government job.

Two strong candidates, both respected lawyers with broad civic experience, are running to replace him. In our view, the better bet is Richard “Rip” Sullivan, a Democrat.

First a word about Mr. Sullivan’s Republican opponent, David Foster. Mr. Foster served eight years on the Arlington School Board (including two as chairman) and four on the state Board of Education as an appointee of former governor Robert F. McDonnell (R), including two as president. He is broadly knowledgeable and committed to public education.

A litigator who heads his firm’s antitrust practice in Washington, Mr. Foster is thoughtful, smooth and politically nimble. In 2009, in an unsuccessful bid for Virginia’s GOP nomination for attorney general, he called himself a “lifelong conservative Republican.” Now, courting a much more liberal constituency, he has scrambled to rebrand himself as a centrist — partly by taking vague, wait-and-see stands on several key issues, including expanding Medicaid and closing abortion clinics.

The thrust of Mr. Foster’s campaign has been to attack a proposed streetcar project, which he believes is unaffordable and likely to worsen traffic. In fact, the controversial part of the project, on Columbia Pike in Arlington, isn’t in his district; moreover, the state legislature would be an unlikely venue for derailing it. Mr. Foster’s strategy seems designed mainly to shift attention away from tough votes he would actually cast as a lawmaker, where his conservatism might not sit well with the district’s constituents.

By contrast, Mr. Sullivan has taken forthright stances in favor of stricter gun control and insuring hundreds of thousands of Virginians by expanding Medicaid and against regulating abortion clinics out of existence. Bright, even-keeled and civic-minded, he has been heavily involved in promoting legal services for the poor, voting rights and affordable housing, among other issues.

On the streetcar project, Mr. Sullivan says, with reason, that there is little the legislature could do beyond authorizing a nonbinding referendum for voters in nearby jurisdictions, which he supports, as does Mr. Foster.

There’s no doubt both candidates are intelligent and qualified for the job. But the contrast is clear: Mr. Foster is a shape-shifter; by contrast, voters would know what they were getting with Mr. Sullivan.

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