November is still a long way away, but all signs seem to suggest Democrats can expect to do quite well in the midterms. FiveThirtyEight’s average of generic ballot polling currently gives Democrats a lead of more than 6 percentage points over the GOP. Major forecasters have been shifting their race ratings in the Democrats’ favor for months and the party has consistently outperformed Hillary Clinton’s 2016 numbers in the special elections that have happened over the past year. The idea that the Democrats have a real shot at actually winning a majority in the House, specifically, is so strong that the rank-and-file are already threatening upheaval in the party’s leadership should they fall short. “It will be an intraparty war,” Rep. Alcee Hastings told Politico in February. “That’s what you can expect.”

To win a majority, the Democrats will need to keep the 194 seats they hold currently and flip at least 24 Republican seats. As the New York Times pointed out Monday, there are 25 Republican-held districts where Hillary Clinton beat Donald Trump in 2016. That’s promising. The popular vote arithmetic is not. It took a 5.4-percentage-point lead in the national congressional vote for Democrats to gain the 31 seats they won in the last Democratic wave in 2006. Republicans held over 55 percent of the seats in the House after 2016’s elections despite winning only 49.9 percent of the popular vote.

This mismatch is nothing new. It’s a function of not only partisan redistricting processes, but also the fact that Democratic and Republican voters wouldn’t be evenly distributed even absent gerrymandering. Still, the Republican redistricting that took place after the 2010 census has had a serious impact. In a December post for Larry Sabato’s Crystal Ball, Alan Abramowitz explained the results of a regression analysis on the relationship between Democratic vote share since 2010 and the number of seats Democrats hold. “In these three elections, Democrats won an average of 21 fewer seats in the House than they would have won in earlier elections given the same share of the national vote,” he wrote.

On Monday, a report from the Brennan Center for Justice reignited the debate over exactly how much Democrats would need to win by, in order to retake control of the House. “To attain a bare majority,” Brennan’s Laura Royden, Michael Li, and Yurij Rudensky wrote, “Democrats would likely have to win the national popular vote by nearly 11 points.”

As gerrymanders become ever more sophisticated, generic ballot leads no longer effectively predict how many seats a party might pick up. Some state maps are carefully designed to withstand significant electoral swings while others respond more nimbly to shifting political preferences. Thus, even if 2018 sees a fairly consistent — and even sizable — national shift in favor of Democrats that is replicated in the states, the party’s seat yield is likely to vary significantly between gerrymandered and non-gerrymandered states.

Again, there have been quibbles about the actual numbers. Abramowitz thinks the Democrats will need to win by at least 4 points, Dave Wasserman of the Cook Political Report thinks that Democrats will need to win by 7. The bottom line, though, is that Democrats will need to absolutely run the table to take the House back in November, and will likely continue to need to do so until a real movement to beat back Republican redistricting heats up.

The courts offer a few glimmers of hope. In January, Pennsylvania’s Supreme Court struck down a district map that, according to the Brennan Center, required Democrats to win over 55 percent of the state’s popular vote to win a third of its seats. The Supreme Court will have two opportunities this year to take up the question of whether partisan redistricting is even constitutional. And Democratic leaders and donors have invested in the National Democratic Redistricting Committee, a group fronted by former Attorney General Eric Holder and endorsed by Barack Obama that is putting money into state races that could break Republican hegemony in the 26 states where they currently control government completely. Incidentally, Democrats control state government in only eight states. In the near term though, Democrats will have to content themselves with galvanizing voters and hoping, specifically, for the best— nothing less will really do.