REP. JOAN Brady describes her role as bringing attention to issues that are not on the House Republican Caucus’ agenda, and serving as “a conduit with my Republican colleagues to make them understand that not every issue is Republican or Democratic.”

That means pushing through legislation to require state government buildings to be more energy-efficient, to prohibit insurance companies from dropping coverage for victims of criminal domestic violence, to outlaw teen sexting, to make it easier for foster parents to adopt abused or abandoned children. It means championing proposals to increase childhood immunizations and fight childhood obesity. These aren’t the macro issues that we like to talk about — tax and education policy, governmental structure — but they’re important measures that need someone who can promote them effectively.

Her Democratic challenger in the House District 78 race in Richland County, Beth Bernstein, describes the incumbent as a lot of talk and not much action, as someone who hasn’t been a strong enough advocate for causes they both support.

If you feel like you’ve already seen this movie, you’re right. It’s also playing in the Richland County Senate District 20 race, where another Democrat is running what feels more like a primary than a general election race, against Senate President Pro Tem John Courson — not stressing differences on issues but challenging the incumbent’s passion and effectiveness.

Although Ms. Brady doesn’t have the influence or visibility that Mr. Courson does, their values are similar — both their support of education and the environment and other mainstream issues and in building coalitions within and across party. Also like the senator, Ms. Brady has managed the unusual feat of winning support from such liberal groups as the S.C. Education Association and the Conservation Voters of South Carolina as well as such conservative groups as the S.C. Chamber of Commerce and the National Federation of Independent Businesses.

Ms. Bernstein strikes us as a sincere, well-meaning person who is running because she thinks she can improve a bad situation at the State House. She is not as knowledgeable about legislative issues as we would have expected, given that she is one of the state Democratic Party’s priority candidates, but she does seem to be a quick study and to have good instincts. What she doesn’t have is a particularly good reason for voters to replace Ms. Brady.

Her criticism of the incumbent for not finding Gov. Nikki Haley guilty of violating campaign laws falls flat, because our laws are so porous that nothing that has come to light indicates that the governor actually violated them. To the contrary, what we know demonstrates that we need to toughen those laws, which Ms. Bernstein champions and Ms. Brady says she supports.

Both candidates support comprehensive tax reform and giving the governor more authority to run the executive branch. Both support better funding public education, though neither knows how to do that, and both oppose paying parents to send their kids to private schools. In fact, apart from Ms. Bernstein greater openness to tax increases — which neither says she supports — it’s hard to find much difference in their positions on important issues.

So the question is how effective each candidate could be in the Legislature, and how the election of either would affect the dynamics in the Legislature. And on both points, Ms. Brady wins.

Ms. Brady seems almost resentful that Democrats would take her on, given her support for so many causes that they champion, when she asks: “Why should it matter if I’m a Republican?” But it’s an excellent question. As long as the House is overwhelmingly Republican, it’s probably more effective to have a Republican representative championing those issues than a Democrat.

We already have lost too many mainstream legislators in both parties, leaving the General Assembly increasingly polarized and its members fixated on growing the number of like-minded lawmakers rather than finding common ground with the ones who are there. The last thing we need to do is to lose the ones we still have — or discourage the ones who remain.