That could change. A federal court panel ruled last month that Republican lawmakers in Wisconsin had intentionally redrawn state legislative district lines in such a blatantly partisan way that the maps violated the Constitution. “There is no question,” the court wrote, that the new maps, which were created in 2011, were “designed to make it more difficult for Democrats, compared to Republicans, to translate their votes into seats.”

In 2012, the year after the new lines were drawn, Republican candidates for the Wisconsin Assembly won less than half of the statewide vote — but 60 of the Assembly’s 99 seats. That pattern persisted in 2014, as well as in federal and state races elsewhere around the country. In North Carolina, Democrats got 51 percent of the 2012 vote for the United States House of Representatives, which translated to only four of the state’s 13 congressional seats. The skew was roughly the same in Pennsylvania: Democrats won a little more than a quarter of the House seats, even though they got a majority of the votes cast in congressional races in the state that year.

Republicans achieved this effect in Wisconsin, according to the plaintiffs in that case, with two tactics: dividing Democratic neighborhoods among multiple districts so that Democratic voters fell short of a majority in each one and, in other places, cramming Democrats into a few districts to dilute their votes statewide.

Both Democrats and Republicans have tried to tilt the playing field when they’ve had the chance. But Republicans, who swept into power in statehouses in recent years, have done much more of it lately, and they have had the benefit of increasingly powerful mapping software to make partisan line-drawing even more precise and effective at protecting their party’s seats. The result is “the most extreme gerrymanders in modern history,” according to a paper published in The University of Chicago Law Review last year.

The paper, co-written by Nicholas Stephanopoulos, a law professor who represented the Wisconsin plaintiffs, argued that courts could address partisan gerrymandering with a measure called the “efficiency gap” — a relatively simple formula that compares each party’s “wasted” votes. Using that measure, the court in the Wisconsin case found that the new maps resulted in so many more wasted votes for Democrats than for Republicans that they violated the First Amendment and the Equal Protection Clause. The court declined to rule on a remedy.