With well more than 100 competitive House and Senate contests happening on Tuesday, keeping track of the big picture on Election Day could seem pretty daunting.

But as polls close, starting at 6 p.m. ET on the East Coast, we’ll start seeing voter data that could give us a sense of how each party is faring — and how real a potential blue wave might be.

The NBC News Political Unit has identified key races — at each poll closing time throughout the night — that will tell the story of election night 2018 as it evolves. These aren’t always the races with the biggest drama or the most compelling candidates (although some are!), but they’re the ones we’ve identified as being the most informative about the political landscape.

Keep in mind: Democrats need a net gain of 23 seats to gain back control of the United States House, while they need a net gain of two to gain the majority in the Senate. Democrats are favored by most analysts, including NBC News, to reach their goal in the House; Republicans have the advantage to maintain their dominance in the Senate.

6 p.m. ET poll close

Kentucky 06: The first competitive race to see polls close on Election Night is also one of the country’s most closely watched. Democrats believe they have one of their best candidates of the cycle in this Lexington-area district in Amy McGrath, a retired Marine Lieutenant Colonel who was the first female Marine to fly in an F-18 on a combat mission. She’s running against incumbent GOP Rep. Andy Barr in a district that picked Donald Trump by 16 points in 2016.

The vote will give an early indication of whether voters in GOP-leaning districts are looking for change or sticking with the GOP. But there’s a caveat: McGrath’s personal story has gotten so much press — and the attack ads against both candidates have been so overwhelming — that this race could end up illustrating national trends OR bucking them.

7 p.m. ET poll close

Georgia Governor: In one of the most closely-watched gubernatorial races of the cycle, Democrat Stacey Abrams faces conservative Republican Brian Kemp in her attempt to become the first female African-American governor in U.S. history. It’s a stark contrast. Abrams has celebrated her history-making candidacy, campaigned with Oprah Winfrey and emphasized education and criminal justice issues.

Kemp won his contested GOP primary largely by embracing President Donald Trump and highlighting his positions on gun rights and illegal immigration. Abrams’ path to victory will require huge turnout of African-American voters who often aren’t engaged in midterms — as well as big numbers with more affluent and well-educated white voters in the state who are fed up with Trump. A win for her could also mean House pickups for Democrats in two seats in the Atlanta suburbs.

Indiana Senate: Democrat Sen. Joe Donnelly and Republican Mike Braun aren’t the most charismatic of the 2018 candidates, which makes this race a good barometer of how a relatively generic Democratic incumbent fares against a generic Republican in a red-leaning state. Donnelly is still fairly popular in the state, but he’s still running neck-and-neck with Braun. If he looks poised for defeat early in the night, Democrats can probably wave goodbye to their slim hopes of winning back the Senate.

Virginia 07: Republican Rep. Dave Brat may be too conservative for this Richmond-area district, which is home to the kind of affluent suburban voter who’s not pleased with Trump. He faces former CIA officer Abigail Spanberger. Early returns could be an indication of whether suburbanites want to use their vote to protest the things they don’t like about Trump or to reward Republicans for a booming economy.

Virginia 10: Republicans looking for a sign that they’ve got a prayer of keeping the House have to hope that Rep. Barbara Comstock — who’s known as a good candidate in a very bad district for a Republican in the Trump era — holds on to her seat. Comstock has tried to distance herself from Trump in this quickly diversifying and well-heeled area. If she’s able to even keep it close, Republicans will breathe a sigh of relief. If it’s a blowout, Democrats will feel like they’re starting the night right where they need to be.

8 p.m. ET poll close

Florida Governor: Democrat Andrew Gillum wasn’t the Democratic establishment’s first choice as a gubernatorial nominee, so it’s ironic that his candidacy could be what pulls Senate incumbent Bill Nelson over the finish line instead of the other way around. If Gillum, who is black, wins over Trump-aligned Ron DeSantis, it’ll be a huge coup for Democrats in a swing state, and it’ll send a message about diversity and resistance to Trump in a state that’s must-win for him in 2020. If he struggles, that’s bad news for Nelson and for Democrats in the state’s eight competitive House races.

Maine 02: Democrats have tried to defeat incumbent GOP Rep. Bruce Poliquin in the last two cycles to no avail, but — as in other competitive seats — they feel more confident about their candidate this cycle. Jared Golden (D), a 35 year-old state representative who enlisted in the Marines after 9/11, is a bit in the mold of Conor Lamb — he’s said he won’t back Pelosi, he touts his bipartisan cred as a onetime aide to Republican Sen. Susan Collins, and he’s used a firearm as a prop in several ads. Both Republicans and Democrats point to this race as a bellwether

New Jersey 03: Health care has been a defining issue of the midterms, and the center of the debate may be in south central New Jersey. This retiree-rich part of the state voted for Trump 51 percent to 45 percent in 2016. Incumbent Rep. Tom MacArthur (R), who was first elected in 2014, was a player during the Obamacare repeal negotiations, when he brokered a compromise between his own moderate GOP wing and conservatives to pass a repeal bill that ultimately failed in the Senate.

MacArthur’s work to dismantle Obamacare — even if his efforts favored a compromise bill that wasn’t as harsh as conservatives wanted — has haunted him during his campaign against Democratic challenger Andy Kim, a national security adviser in the Obama White House. If Kim wins, it’s hard to see how Democrats don’t win back the House.

Tennessee Senate: If Democrats have a prayer of winning back the Senate, they’ll almost definitely need to win in three GOP-held states: Arizona, Nevada and Tennessee. (That assumes that North Dakota Democrat Heidi Heitkamp loses her re-election bid.) Democratic candidate Phil Bredesen is a well-liked former governor who enjoys more popularity — but lower head-to-head poll numbers — than GOP opponent Marsha Blackburn. An early loss for Bredesen wouldn’t completely seal Democrats’ fate, but it would leave only two highly unlikely paths to Democratic victory: An unexpected win for Heitkamp or a long shot loss for Ted Cruz in Texas.

9 p.m. ET poll close

Arizona Senate: Arizona’s Senate contest between Democrat Kyrsten Sinema and Republican Martha McSally isn’t just a must-win for Dems — it’s a good barometer of how Latino turnout may look in other key states. High participation for Latinos may be great news for Democrats in neighboring Nevada as well as California’s competitive House districts.

Minnesota 01: Republicans are hoping for a rare pickup opportunity in this southern Minnesota district, which went for Trump by a whopping 53 to 38 percent. Republican Jim Hagedorn, the son of a former congressman, has run for the seat three times before. He faces former Deputy Assistant Secretary of Defense Dan Feehan.

Outside groups have hammered Feehan relentlessly, including with TV ads featuring Colin Kaepernick and George Soros. If Republicans don’t win here, they’re probably having a rough night. This is one of four competitive seats in the state — two held by Republicans and two by Democrats; a net gain of one seat for either side out of Minnesota probably signals how the race is going nationwide.

Minnesota 02: Incumbent Republican Rep. Jason Lewis barely beat Democratic rival Angie Craig (D) in 2016, and the two are back for a rematch this cycle. Lewis took heat this year when journalists unearthed controversial comments he made about women and LGBT people (Craig is gay) on his conservative radio show. Between those comments, Lewis’s pro-Trump voting record and the president’s sinking approval in the state, Craig has a good shot here. The gender gap here could be a headline.

New York 19: This Catskills-area district swung hard for Trump in 2016 after going for Barack Obama by six points in 2012. Democrats nominated Rhodes Scholar and Harvard law graduate Antonio Delgado to face Republican John Faso. Republican attacks on Delgado from outside groups have almost exclusively focused on rap lyrics Delgado, who is black, wrote a decade ago. Polling in the race hasn’t been conclusive, but this is the kind of district where Democrats could start building a substantial majority if Delgado wins.

Texas Senate: Plenty of ink has been spilled about race between Democrat Beto O’Rourke and Republican Ted Cruz, so we won’t relive it here. We’ll be very surprised if O’Rourke gets within 2-3 points of Cruz, but there are two things to watch here: How much O’Rourke’s star power in urban areas boosts Democrats in competitive Houston and Dallas-area House races, and how much of the electorate is made up of Latinos. (In 2014, it was just 17 percent, compared to 24 percent in 2016.)

11 p.m. ET poll close

California 45: There are more than 10 House races to watch in California — many in the Orange County area and several that went for Hillary Clinton in 2016. Maybe the most revealing one is Rep. Mimi Walters’ seat in the inland O.C. Republicans early on thought Walters was doing all the right things to stay safe despite the district’s recent blue tinge, but Democrat Katie Porter has relentlessly messaged on Walter’s health care and tax bill votes. California is slow to count votes, but this may be the race that launched a thousand think pieces on Nov. 7.

Washington 08: Republican candidate Dino Rossi is hoping that this is finally his year. A failed candidate for two statewide offices in the last decade, Rossi has been well-funded in his attempt to fill the open seat of retiring Dave Reichert. But this is still a district that voted for Clinton by three points, and Democrats have tried to paint Rossi as a de facto incumbent. That’s a contrast to their candidate, newcomer and pediatrician Kim Schrier, who’s posted huge fundraising numbers. This is another race where voters in a largely suburban area will choose between a familiar Republican and a newcomer Democrat.