"Now we can say with certainty: Every vote counts," declared Ralph Northam, Virginia's Democratic governor-elect, last week. He was referring to the still-disputed contest for the 94th district in Virginia's House of Delegates.

After a recount, Democrat Shelly Simonds appeared to have won the race by a single vote. Then a three-judge panel awarded a disputed ballot to Republican David Yancey. The race is now tied, at least for the time being. If Simonds prevails, Democrats will gain a 50th seat in the House—forcing Republicans into a power-sharing arrangement.

Thus control of the House hangs on a single ballot. Little wonder that Northam says every vote counts—or that plenty of others agree:

"Every vote counts: 1 more ballot ties up Virginia House race," reported CNN.

"Every Vote Counts: VA House Of Delegates Now Split 50-50," claimed a writer for TownHall.com.

"The moral of the story? Every vote counts," concluded a piece in New York magazine.

There are many more examples, but you get the drift.

What's more, as Bloomberg columnist and Yale law professor Stephen L. Carter noted recently, other races have come down to a single vote, albeit not often: "A 2002 paper by economists Casey B. Mulligan and Charles G. Hunter analyzed 16,577 elections for the U.S. House of Representatives between 1898 and 1992 and found only one contest, in nearly a century, that was decided by a single vote… When they studied state legislative elections, they found nine more."

Here in Virginia, the Daily Press' David Ress recalls an instance in 1991, "when a recount gained Del. Jim Scott, D-Fairfax, a net 18 votes, turning his loss into victory by giving him a one-vote edge over Republican David Sanders—and the moniker 'Landslide Jim.'"

Case closed: The record proves that every vote can count. But as much as we'd like to think that's always the case, it isn't. In fact, a current challenge before the Supreme Court is premised on proving that a great many votes do not count at all.

The case concerns partisan gerrymandering in Wisconsin. The Supreme Court has ruled racial gerrymandering unconstitutional. But it has always maintained that partisan gerrymandering lies outside the court's purview, so any remedy for it must come from legislators—i.e., from the very people who perpetrate it. Good luck with that.

Challenges to partisan gerrymandering have faced another obstacle: finding what Justice Anthony Kennedy has called a "workable standard" for judging when redistricting plans cross the line between constitutional and unconstitutional. The suit in Wisconsin relies on what reformers hope will become such a standard: the efficiency gap.

What's that? As The New York Times explains: "In general, the goal of a partisan gerrymander is to force the other side to 'waste' votes, and that's exactly what the efficiency gap measures. A wasted vote is one that doesn't contribute to winning any additional districts. All of the votes beyond what's necessary to win a district are 'wasted' in victory. All votes are wasted in defeat, since they didn't result in any seat at all."

To find the efficiency gap, you add all the votes for the losers in a state's legislative races and all the surplus votes for the winners, then divide by the total number of votes. The creators of this measurement suggest using a 7 percent efficiency gap as the demarcation line between constitutional and unconstitutional gerrymandering. (It's not clear why 7 percent should be the magic number. But there has to be some magic number, and 7 percent might be as good as any other.)

In Wisconsin, the efficiency gap for the past three congressional elections has ranged from 10 percent to 13 percent in Republicans' favor. Three years ago, the GOP won 52 percent of the statewide vote—but 63 seats in the Wisconsin Assembly. In Maryland, the efficiency gap in congressional elections is 10.7 percent in Democrats' favor. So Democrats control seven out of eight seats in the House of Representatives, even though they won only three out of five votes statewide.

Ideally, of course, every vote should matter: Elections should be competitive, and the ratio of Democratic to Republican winners should track the ratio of Democratic to Republican votes. But that's not always possible, especially in statewide races. (The gubernatorial vote might split 60-40, but there's only one governor.) What's more, the efficiency gap can make fair maps look unfair in heavily partisan areas. Detroit tends to vote for Democrats by a 9-1 margin, but not because anybody gerrymandered Democrats into the city.

Yet the wish that every vote should always count does not mean every vote always does. And if the Supreme Court rules against Wisconsin's gerrymander and adopts the efficiency-gap test, then the notion that some votes are wasted in every election will no longer be a mere theory. It will be the law of the land.