Updated: 8:38 p.m.

Conservative Justice David Prosser surged ahead of his left-leaning challenger Thursday in the unusually high-profile race for the Wisconsin Supreme Court after a counting error was discovered, the Milwaukee Journal Sentinel reported.

Waukesha County officials revealed the error during a news conference two days after polls closed in the election, which was largely seen as a referendum on Republican Gov. Scott Walker’s crackdown on state employee labor unions.

Prosser’s challenger, state prosecutor JoAnne Kloppenburg, led by slightly more than 200 votes Wednesday, when officials believed all votes had been tallied. Nearly 1.5 million votes were cast in Tuesday’s contest.

But Wednesday’s totals did not include complete returns from heavily Republican Waukesha County, according to local officials. County Clerk Kathy Nickolaus said that officials realized during a review that she failed to save the 14,315 votes cast in the city of Brookfield to a database. The Brookfield votes increased Prosser’s total by 10,859 and Kloppenburg’s by 3,456.

“The purpose of the canvass is to catch these kind of mistakes,” Nickolaus said. She apologized, saying human error is “common in this process.”

Prosser’s lead now stands at roughly 7,000 votes, although the numbers are expected to vary slightly as all counties review their totals.
 
It was immediately unclear whether Kloppenburg, who had declared victory Wednesday, would seek a recount or whether the margin of victory requires an automatic recount.

The Supreme Court contest, conducted as part of the usually sleepy Badger State’s spring elections, attracted national attention and millions of dollars from outside groups.