Democrats are slight favorites to flip the Senate, though Republicans have a clearer path to keep the upper chamber of Congress than the White House.

Democrats, meanwhile, are likely to add to their once-fragile House majority, as Republicans will likely cede additional ground in the follow-up to the 2018 midterm wave.

The forecast is the result of a year-long reporting project, based on conversations with dozens of strategists, operatives and pollsters, in addition to examining public and private polling, voting trends and campaign finance and advertising data.

The most challenging element of the forecast is gauging the effect of varying turnout across the map and countervailing trends regarding voters’ access to the ballot box. A combination of expanding absentee and in-person early voting, along with an explosion of interest in this election, means turnout is expected to be much higher than in 2016.

That’s already true in Texas, where more ballots have been cast in early voting than in the entire 2016 election.

At the same time, there are questions about how many votes will actually be tallied. The multi-fold increase in mail ballots in this election means there will be significantly higher rejection rates. Mail slowdowns could affect the timely delivery of the ballots in some key places. Republicans, led by Trump, are working to restrict the acceptance of mail ballots in a number of states, especially those where officials liberalized the rules around absentee voting in response to the coronavirus pandemic or problems at the postal service.

Those factors are more difficult to quantify, and they add some uncertainty to the outcome.

President

: Lean Democratic

The latest forecast continues to show 279 electoral votes leaning toward Biden, just above the 270 he needs to win the presidency. Trump, with 163 electoral votes leaning his way, still needs to win all of the toss-up states, totaling 96 electoral votes, then add at least one Democratic-tilting state.

The toss ups are Arizona, Florida, Iowa, North Carolina, Ohio, and a new entrant: Georgia.

Democrats are optimistic about their chances in Arizona, where they are relying heavily on strong Latino turnout and the continued break of the suburbs away from Republicans. It’s a difficult state to poll, and there is enough doubt for it to remain as a toss-up.

It looks like another photo finish in Florida, where the polls show an essentially tied race. A Biden victory would likely be the result of a trade: ceding some ground among Hispanic voters, especially in South Florida, while performing stronger with white seniors, who have been most affected by the coronavirus pandemic.

Both parties think the race is tighter in Iowa than this weekend’s Des Moines Register/Mediacom poll showed, and Biden’s 11th-hour visit to Ohio suggests his campaign believes it has a chance to head off Trump in another state where voters broke sharply for the Republican last time.

Georgia is a new addition to the toss-up column, and polls show Trump and Biden deadlocked there. Both men visited in the final week of the race, and former President Barack Obama will be there to stump for Biden on Monday.

By comparison, Biden generally leads Trump in the polls in North Carolina, though the race is considered close to a coin flip.

Even if Trump sweeps these toss-ups and holds all his states — including Texas, which remains in the Lean Republican column despite some close polling data and robust early-vote numbers in Democratic-leaning areas — he still needs at least one of the Lean Democratic states.

His best chance appears to be in Pennsylvania, where the closing round of high-quality polls shows a mid-single-digit lead for Biden. Neither campaign is leaving anything to chance: Biden is spending the final two days there — minus a quick jaunt to Cleveland — while Trump visited Saturday and is coming back on Monday.

Biden’s polling leads are a little larger in Michigan, Minnesota and Wisconsin — the three other Lean Democratic states bordering the Great Lakes. But the process in some of these states could get messy.

The president’s bluster about excluding mail ballots that are tallied after Tuesday night runs counter to U.S. law and democratic norms. But there are also practical things Trump and the GOP are doing to restrict mail voting in Pennsylvania and Wisconsin, specifically, that could disqualify more Democratic votes than Republican ones, based on the partisan gap in voting method this year. Democrats are far likely to say they intend to vote absentee, while Republicans are significantly more inclined to vote in-person on Tuesday.

In Wisconsin, the Supreme Court has already ruled that mail ballots that arrive after Election Day can’t be counted, regardless of whether they were postmarked before the polls close. And the GOP is aiming to get the court to deliver a similar ruling for Pennsylvania ballots after Election Day, which could exclude more Biden votes than Trump votes and boost the president’s reelection odds.

Outside of the Great Lakes states, Nevada and New Hampshire are also in the Lean Democratic column — but both have received less attention from the candidates.

In the event of a close Electoral College count, the two states that split their electoral votes by congressional district could be decisive. The Omaha-based, largely suburban 2nd District in Nebraska is leaning toward Biden, while Maine’s swingy, mostly rural 2nd District is a pure toss-up.

Senate

: Toss-Up

The Senate math is simple: Democrats need to net three seats if Biden and Kamala Harris win on Tuesday, four if Trump and Vice President Mike Pence are reelected.

Few give Sen. Doug Jones much of a chance in Alabama, setting Democrats back another seat. But Arizona — where appointed GOP Sen. Martha McSally has closed some but not enough of the gap against Democrat Mark Kelly — and Colorado are leaning in their column.

The path then turns to five toss-up states, where races are within the margin of error. In Maine, GOP Sen. Susan Collins and Democrat Sara Gideon are running neck-and-neck. But put a tiny thumb on the scale for Gideon: Most observers expect Collins to be felled by the state’s ranked-choice voting scheme, which allows voters to rank their candidates for an instant-runoff tabulation after Election Day should no one get a majority of the vote.

With a win in Maine, Democrats would still need at least one more seat. North Carolina is their next best option. Even following a sex scandal last month, Democrat Cal Cunningham is tracking close with the top of the ticket — and a Biden victory there would be difficult for GOP Sen. Thom Tillis to overcome. But while Cunningham outperformed Biden before the scandal, he would likely be swamped now by a Trump win.

GOP Sen. Joni Ernst had a slight edge in Saturday’s Iowa poll, though both parties think her race against Democrat Theresa Greenfield is on a knife’s edge. Steve Bullock, the term-limited governor of Montana, needs to outrun the top of the ticket to oust GOP Sen. Steve Daines. Polls show the Montana race roughly tied.

As with the presidential race, the newest contest to join the toss-up category — moving from Lean Republican — is the race in Georgia between GOP Sen. David Perdue and Democrat Jon Ossoff. Perdue once led Ossoff in the polls, but a coronavirus stock-trading scandal (Perdue says he was cleared of any wrongdoing) and an embarrassing moment at a Trump rally in which he mocked the pronunciation of Harris’ first name has the race tied now. An obstacle for both candidates: The winner must earn a majority of the vote — there’s a Libertarian candidate also on the ballot — or the race goes to a January runoff.

Similarly, the special election for Georgia’s other seat is remaining in the GOP’s column for now, since no candidate is expected to earn a majority, and appointed Sen. Kelly Loeffler will still likely be serving on the day the new Congress meets next January. But Loeffler and Rep. Doug Collins are locked in a tight race to the right to earn the second spot in the special-election runoff against Democrat Raphael Warnock.

Beyond the core Senate map, Democrats have made inroads in red states like Alaska, Kansas and South Carolina. But those contests are remaining in the Lean Republican category, as polls have showed GOP voters coming home in the closing weeks. Similarly, both parties are spending tens of millions in Michigan. But Democratic Sen. Gary Peters still leads Republican John James — who needs Trump to make the state very close, at minimum — in the polls.

The conventional wisdom is that most of the Senate toss-ups typically break in the same direction. But that wasn’t the case last cycle. As we do now, POLITICO rated five races as toss-ups in 2018. Republicans won three of them, and Democrats won two.

House

: Likely Democratic

Not only are Democrats favored to keep the House majority — they’re likely to gain seats.

Including vacancies in safe seats, Democrats currently hold 234 of the 435 House seats. Our final forecast has 228 seats leaning toward Democrats. That means they would only need to win six of the 27 toss-up races to maintain the size of their majority.

A roughly even split of those toss-ups would result in a five-to-10-seat Democratic gain, though an outcome outside that narrow range is possible.

The latest changes move eight seats that had been rated as toss-ups into the Lean Democratic column, including districts in places where Democrats have gained ground in the Trump era: Orange County, Calif.; the suburbs of Atlanta, Dallas, Philadelphia and Charleston, S.C.

Meanwhile, three seats move from Lean Republican to toss-up — most notably the expensive race in central Texas between GOP Rep. Chip Roy and former Democratic gubernatorial candidate Wendy Davis.

Of the 17 races shifted Monday, 16 are toward Democrats. But the one that goes toward the GOP would be a special prize for the party if it can win. Cheri Bustos, the chair of the Democratic Congressional Campaign Committee, is facing a tougher-than-expected race for her northern Illinois seat, which Trump carried narrowly in 2016. House Majority PAC, Democrats’ top super PAC, spent roughly $1 million over the final week to air TV ads there. Her seat moves from Likely Democratic to Lean Democratic.

Governors

The gubernatorial landscape is unlikely to be altered significantly in this year’s elections.

In the largest state holding an election for governor, North Carolina, Democratic incumbent Roy Cooper has consistently led his GOP opponent, Lt. Gov. Dan Forest.

Forest has made Cooper’s response to the coronavirus pandemic a centerpiece of his campaign, pledging to reopen the state much faster and revoke Cooper’s mask mandate. But polls show voters give Cooper high marks for his handling of the crisis, and Forest lags behind Trump and Tillis on the ballot. The race remains in the Lean Democratic category.

The second-largest state up this year is Missouri, where GOP Gov. Mike Parson is facing a spirited and expensive challenge from Democratic state Auditor Nicole Galloway. The race is competitive, but Parson — whom Galloway has hit for being too lax on the virus and opposing the state’s voter-approved Medicaid expansion — is the favorite in a Lean Republican race.

In Montana, GOP Rep. Greg Gianforte, who lost to Bullock in the 2016 race, is hoping to ride Trump’s coattails in the open-seat contest. It’s another close race, but with a Republican lean.

The lone ratings shift is in New Hampshire, where GOP Gov. Chris Sununu is well-positioned for a third two-year term, despite the blue tilt of the Granite State this year. Democrat Dan Feltes, who didn’t win the nomination until a September primary, has failed to close a wide gap in the polls; the race moved from Lean Republican to Likely Republican.

Despite a quiet year for governorships in 2020 — 38 of them will be up for grabs in 2021 and 2022 — there is plenty at stake in state governments. The parties are scrapping for control of a number of state legislature chambers that could reshape the policy and political landscapes across the country with redistricting on tap, beginning next year.