Virginia Del. Robert G. Marshall (R-Prince William). (Steve Helber/AP)

WHAT WOULD otherwise be a small-stakes race for a low-profile electoral office — the Manassas-area 13th District seat in Virginia's House of Delegates — has taken on national dimensions and attracted national cash largely because the Democratic challenger, 32-year-old Danica Roem, would become the state's first openly transgender elected official. That's given the 13-term Republican incumbent, Del. Robert G. Marshall, an opening to portray her as an extremist. In fact, as Mr. Marshall has shown repeatedly during his 25 years in office, he is the extremist in the race.

Mr. Marshall, 73, wields a scholarly affect to distract voters from his long-standing legislative priorities, which include a laundry list of hard-right conservative causes that has prompted lawmakers of both parties in Richmond to refer to him as "Sideshow Bob." A relentless culture warrior, Mr. Marshall was a bitter opponent of same-sex marriage; has championed a legislative push to enact a Virginia version of North Carolina's notorious bathroom bill, restricting public restrooms based on birth gender rather than identity; and has been a crusader against abortion as well as birth control.

In 2010, he managed to create a furor even among his own party's leadership by suggesting that God exacts vengeance on women who abort their fetuses by ensuring that their subsequent pregnancies will produce disabled children. "There's a special punishment Christians would suggest," he said, conflating contempt for women who seek abortions with disdain for those with disabilities.

During the current race, he has refused to debate Ms. Roem, asserting high-mindedly that no fair exchange of views is possible because her supporters have insulted him by referring to him as "Bigot Bob." But is that an inaccurate characterization of an official who opposed the judicial nomination of a respected gay prosecutor and proposed legislation to ban gays from serving in the Virginia National Guard? He justified the latter stance under the following rationale: "It's a distraction when I'm on the battlefield and have to concentrate on the enemy 600 yards away and I'm worried about this guy who's got eyes on me."

Predictably, Mr. Marshall has tried to cast doubt on the legitimacy of Ms. Roem's gender identity, insisting on using male pronouns to refer to her. Conservative groups backing him have unleashed incendiary robo-calls suggesting that girls' sports teams would be infiltrated by boys under policies favored by Ms. Roem and charging that she would pursue a radical agenda.

In fact, Ms. Roem, a former journalist with a wonky streak, has largely focused her campaign on proposals to ease traffic congestion along Prince William County's Route 28 corridor, an area of vulnerability for Mr. Marshall, who opposed the state's bipartisan landmark transportation funding package in 2013.

While the attacks on Ms. Roem focus largely on her identity, Mr. Marshall's shortcomings involve the intolerance of his ideas. In an era of rising extremism, Mr. Marshall remains a standard-bearer of zealotry whose aversion to pragmatism promotes legislative dysfunction.