The Democratic Party is going all in on Georgia. More than $8 million in outside donations and 7,000 volunteers have come to the aid of Democrat Jon Ossoff, who is hoping to clear the 50 percent mark during Tuesday’s special election in the Atlanta suburbs.

Liberals see a lot riding on the race. A win would deliver Democrats their first major electoral victory over President Donald Trump and a jolt of momentum to their left-wing base — and it would have added resonance given Democrats’ surprisingly strong finish in a Kansas special election two weeks ago.

A victory could also encourage more Democrats to run for office in conservative districts, and might give Republicans in Washington some pause before continuing to ram through things like their wildly unpopular health care plan.

But whether Ossoff can pull off the improbable upset or not, Democrats will continue to face deep structural disadvantages to reclaiming Congress — most notably, gerrymandered congressional districts and the incumbency advantage that favors those running for reelection.

Unless those change, Democrats will continue to face an uphill battle to winning back the House, even amid an extraordinary surge in grassroots activism among their base.

“This race has been a sugar high for Democrats,” David Daley, author of Ratf**ked: The True Story Behind the Secret Plan to Steal America’s Democracy, a book about Republicans’ 2010 gerrymandering plan, says in an interview. “But the congressional districts were drawn with deep partisan intent, and until Democrats do something about this very deep structural rot, it will be extraordinarily difficult for them to win.”

Democrats are competing on an unbalanced playing field

There’s a reason Democrats are viewed as such underdogs in Georgia’s Sixth Congressional District, even though Hillary Clinton only lost it by a single point: It wasn’t created with the intention of giving Democrats a chance to win it.

If you don’t believe me, listen to one of the Republican politicians close to those who helped draw district lines.

“I’ll be very blunt: These lines were not drawn to get Hank Johnson’s protégé to be my representative. And you didn’t hear that,” said Georgia state Sen. Fran Millar, according to the Atlanta Journal-Constitution, comparing the Georgia Sixth to Johnson’s district, which is majority African American. “They were not drawn for that purpose, okay? They were not drawn for that purpose.”

Since Trump’s inauguration, three special elections to replace former Republican House members have drawn national media attention — the Kansas Fourth District, where Republicans won a seat that they secured in 2016 by 31 points; the Georgia Sixth, where Ossoff is running and which Republicans won last year by 30 points; and Montana’s only congressional district, which former Rep. Ryan Zinke won last fall by 17 points.

These are all long-shot bids for the Democratic Party. The problem for Democrats is that even if these special election districts are not representative of the country as a whole, they are not that far off from the kind of seats Democrats are going to have to take to win back Congress in 2018.

Scholars disagree about exactly why this is. Daley says Democrats have been handicapped primarily by Republicans ruthlessly redistricting congressional districts to disempower Democrats, while others point to self-sorting along ideological lines (with liberals clustering in cities) to explain the fall in swing districts.

Whatever the exact cause, Democrats are almost certainly going to have to peel off a lot of seats that Clinton lost by more than just a point if they want to take back the House, says the University of Virginia’s Kyle Kondik.

Though he lost the popular vote by 3 million, Trump carried 230 congressional districts to Clinton’s 205. The election number crunchers at Daily Kos say that to take the House in 2018, Democrats would have to win all 23 seats held by Republicans that Clinton won, hold all 12 seats held by Democrats that Donald Trump won, and still pick up several more seats.

Another way to understand the scope of the challenge involved is to consider the most left-leaning seat Democrats would have to take to win back the House — the seat that, assuming they won every seat that is more Democratic, would give them back control. Democrats lost that threshold seat (the “median seat”) by a full 12 points, according to Daily Kos. In other words, if every Democratic candidate uniformly improved his or her performance by 12 points, the party would still not take back the House.

Democrats may be right to say that the three special elections don’t reflect the rest of the country. But the reality is that they do look like the House seats they’d need to win back Congress sometime soon if they’re ever going to regain the kind of majorities they had in 2008.

Democrats would need to win the national vote by a lot to take back the House with the current map

Democrats’ structural disadvantage is so steep that they’d almost certainly have to win the national House vote by several million votes to take it back.

Previous wave elections have been able to overcome these kinds of built-in advantages. But that typically requires some kind of major shock to the political system, like the Iraq War or an economic collapse. Consider the following chart from Kondik at the University of Virginia’s Center for Politics — only one year, 2010, has seen as big of a swing as Democrats need now:

House generic ballot in RCP vs. seats gained, 2002-2016. Note where it was in 2006-2008, when Dems took and built on House majority pic.twitter.com/YEzfteZP3f — Kyle Kondik (@kkondik) April 14, 2017

In that year, Republicans were performing more than 9 points ahead of Democrats on what’s called the “generic ballot,” meaning which party people prefer without ever asking about candidates. Polling for the midterms thus far has been scarce, but the best evidence we have so far suggests Democrats are at closer to 3 points, according to Kondik.

He is more skeptical of the impact of gerrymandering than other experts, but he also thinks Democrats would have to be outpolling Republicans nationally by double digits to win back the House. Another election expert, Princeton professor Sam Wang, says Democrats would have to capture the national vote in 2018 by 7 to 12 points to control the House.

There are also the massive obstacles Democrats face in retaking the Senate. As Vox’s Andrew Prokop notes, Democrats’ map for 2018 is abysmal — the party has to defend 25 Senate seats in 2018, 10 of which voted for Donald Trump by 18 points or more. Republicans, meanwhile, only have to defend just eight seats, six of which are in deep-red territory.

The 20-point swing toward the Democrats in the recent Kansas special election does give Democrats some room to hope. If every seat swung that heavily in their favor, then Democrats would gain control of Congress. But the outcome of that race is complicated by the facts on the ground — most notably, that the state’s Gov. Sam Brownback is the least popular in the country.

Of course, that hardly means doing so will be impossible. Democrats were able to win in deeply red territory in 2006 and 2008, when they captured congressional seats and governors’ mansions in Nebraska, Montana, North Dakota, and other traditionally conservative states.

Where Democrats do have a chance to strike back against gerrymandering

Democrats may be making a mistake by spending so much of their resources in Georgia, according to Daley. He notes that there are other ways for the party and its donors to try to reverse the gerrymandering that cripples their chances, whereas Ossoff will have to run for reelection in 18 months.

“Democrats need a short-term play and a long-term play — the long-term play has to be building themselves back up and solving the down-ballot atrophy that’s set in over the past decade,” Daley says.

“I think Democrats are getting distracted by their hope of taking back the House in 2018, which is an extraordinarily uphill fight.”

Most important in this fight, Daley says, is the upcoming Virginia governor’s race in 2017. Winning that race would give Democrats the power to veto the Republican maps in 2020. (Republicans hold seven of the 11 congressional seats in Virginia, even though the state has gone blue in several presidential, Senate, and gubernatorial elections in the past few years.)

Then there’s a slew of upcoming races in 2018 for control of statehouses — Wisconsin, Ohio, Pennsylvania, Florida, Michigan — that Republicans similarly gerrymandered in 2010, Daley said.

Ossoff may give Democrats a valuable boost of energy on Tuesday. But however the race turns out, the real battle to retake the House from Republicans is just beginning.

“Democrats keep thinking they can undo this deep structural rot at the ballot box through electoral politics as usual, but that is not likely to be particularly effective in districts that have been designed with such a thumb on the scale,” Daley says.

Watch: The algorithm that could help end partisan gerrymandering