Everything that happens will set the stage for the 2018 midterm elections, where control of Congress could be on the line.
Here are four major races Tuesday and what both parties have on the line in each of them.
1. Gubernatorial races in Virginia and New Jersey
What's on the line for Democrats: In New Jersey, Democrats have a chance to flip term-limited Gov. Chris Christie's seat. Christie (R) is extremely unpopular, which is one reason Democrats say they're feeling good about their candidate, Phil Murphy. A Murphy win could make New Jersey just the seventh state to be entirely controlled by Democrats, because the state legislature is strongly Democratic.
In Virginia, Democrats are trying to hold on to the governor's seat by their fingertips. A new Washington Post-Schar School poll shows Republican Ed Gillespie closing in on Lt. Gov. Ralph Northam's once-double-digit lead, within five points a week before Election Day. For Democrats, winning here is everything. They need to show they can win a contested race in a state that's leaning blue with an unpopular president from the other party. Historically, Virginia voters have usually voted for the party that is out of the White House.
What's on the line for Republicans: Gillespie has run a race that has echoed Trump, from getting tough on majority-Latino gangs to keeping Confederate statues. If Gillespie wins, Republican operatives will see it as a sign that they've figured out how Republican candidates can embrace Trump's policies without turning off swing voters.
2. House of Delegates races in Virginia
What's on the line for Democrats: Democrats are trying to put a dent in Republicans' 2-to-1 control of the 100-seat House of Delegates. They hope to build off momentum that comes from flipping eight state legislative seats across the nation this year. In Virginia, Democrats think they can make some gains in 17 Republican-held seats that Hillary Clinton won thanks to compelling first-time candidates such as the potential first Latina, Asian American female and transgender state legislators, who are motivated by Trump's election to run.
What's on the line for Republicans: Barring a massive Democratic wave, they will keep control of the state legislature. (Republicans also control the state Senate, which isn't up until 2019.) That means Republicans will control redrawing the congressional and state legislative electoral maps in 2021. If they have a Republican governor to sign off on those maps, they can cement their control of the state for a long time.
3. Washington state special elections
What's on the line for Democrats: Like New Jersey, Democrats are trying to get a governing trifecta — control of both state legislative chambers and the governor's mansion — for the first time here since 2012.
Democrats need to net just one state Senate seat out of a handful of special elections Tuesday, and they will effectively control the chamber. Democrats have zeroed in on a suburban Seattle race that has been in Republican hands for seven years. A jaw-dropping $10 million has been spent there to elect either Democrat Manka Dhingra or Republican Jinyoung Lee Englund.
“This is one of the areas that we frankly, as Democrats, should have had a long time ago,” said Jessica Post, executive director of the state Democratic Legislative Campaign Committee, which helps elect Democrats to state legislatures and has spent $745,000 on this race. “It would be a blue wall on the West Coast if we are able to flip that chamber.”
What's on the line for Republicans: They're excited about possibly electing Englund, who would be the first Korean American woman elected to a state senate in America, and they would be thrilled to keep a blue-ish state out of entirely Democratic hands.
Republicans say the fact that Democrats could lose a close race in a deep-blue state is a sign of Democrats' weakness.
“You're in a competitive race and you have to spend millions and millions just outside the statue of Lenin [in Seattle]," said Matt Walter, director of the state Republican State Leadership Committee, which helps elect Republicans to state legislatures. “When you're doing that, you're trying to claw yourself back off the edge of the cliff.”
4. Georgia state Senate special election
No, Democrats don't have a chance to control any branch of government in deep-red Georgia. But they can play defense by flipping an open state legislative seat Tuesday. If Democrat Jen Jordan can win outright or make it to the December runoff and win, they'll block a GOP supermajority there.
A win in a Republican-held Senate could set up Democrats to seriously play for Georgia’s governorship next year for the first time in two decades, said liberal Daily Kos blogger Carolyn Fiddler. “Next Tuesday is full of electoral opportunity for Democrats all across the country.”
And that's true. From Virginia to Washington state, Democrats have a lot to gain Tuesday. But they also have a lot to prove.