In California, Democrats are hopeful they've avoided the potential nightmare of being locked out of winnable House races due to the state's unique primary system that allows the top two candidates of any party to advance.
Still, some of those races remained too close to call Wednesday morning, with many more ballots to count.
Democrat Gil Cisneros will face Republican Young Kim in California's 39th District, one of several competitive seats in Orange County, a crucial battleground in November's midterm elections, CNN projects.
In retiring Rep. Darrell Issa's 49th District, CNN projects that one Democrat will advance -- though it's still a tight three-way race to see which Democrat that will be.
Those developments were a relief for Democrats, who spent months trying to winnow their larger-than-ever pools of candidates due to California's "jungle" primary.
In two other races -- GOP Rep. Dana Rohrabacher's 48th District and Rep. Jeff Denham's 10th District -- Democrats led for the second spot in the general election, but the races were too close to call. And because California accepts mail-in ballots through the end of this week, as long as they were postmarked by Tuesday, it could take days or even weeks to identify the candidates who advance.
Sen. Dianne Feinstein sailed through her primary and will face Senate Majority Leader Kevin de Le-n in the general election. Former San Francisco Mayor Gavin Newsom advanced to the general election in the governor's race and will face Republican John Cox, who had the backing of President Donald Trump.
Here are six other takeaways from the most important night yet on 2018's political calendar:
Another big night for female candidates
Following a trend that's been clear throughout 2018's primaries, Tuesday was another big night for female candidates, some of whom took steps toward breaking their states' gender barriers.
In California, Young Kim -- the first Korean-American Republican woman to become a state lawmaker there -- advanced to the general election in retiring GOP Rep. Ed Royce's 39th District. If she wins in November, she would be the first Korean-American woman in Congress.
In South Dakota, Republican Rep. Kristi Noem won the primary and is now likely to become the state's first female governor.
In Iowa, Democrats Cindy Axne and Abby Finkenauer could become the state's first female House members.
And in New Mexico, Democrat Deb Haaland's win puts her on track to become the nation's first Native American congresswoman.
Montana's battle of the flat-tops
Montana Democratic Sen. Jon Tester now has his Republican challenger, according to a CNN projection: state auditor Matt Rosendale.
Rosendale's win means the two best flat-top haircuts in politics will face each other in a state where Trump won big in 2016 and where he has made Tester a frequent target.
It was a long way down to Rosendale for Republicans. Initially, Ryan Zinke -- a former congressman who is now Trump's interior secretary -- was national GOP leaders' preference for the seat. Their second choice, attorney general Tim Fox, also passed. That made Rosendale the establishment preference.
Tester's brand has withstood close races before, and Gov. Steve Bullock showed in 2016 that Democrats can win in Montana in the Trump era. But this race will be among Republicans' top targets in November.
Has Bernie's power in Iowa peaked?
Vermont Sen. Bernie Sanders pushed Hillary Clinton to the limit during the Iowa caucus in 2016, a second-place finish that helped launch his upstart presidential run.
Sanders seems likely to run again in 2020 and is now confronted with a critical question: Is the 2016 magic still there?
If Pete D'Alessandro's showing in Iowa's Third Congressional district provides any clues, that answer is no.
D'Alessandro, Sanders' top aide in Iowa during the 2016 caucus, finished a distant third to Eddie Mauro, a former teacher, and Cindy Axne, a former state government official on Tuesday night, according to CNN's projection.
Sanders, who is cautious with his endorsements, went above and beyond for D'Alessandro. He backed his former aide in January, traveled to Des Moines for a rally in February and wielded the power of his sizeable email list to raise money for D'Alessandro.
The email boosted D'Alessandro's fundraising, but did little to help him catch up to Mauro and Axne, who both significantly outraised the former Sanders Iowa aide.
Roby faces GOP wrath for opposing Trump
Alabama Rep. Martha Roby is headed to a Republican runoff to save her seat after failing to top 50% in Tuesday's primary.
Roby, whose criticism of Trump over the "Access Hollywood" tape in 2016 earned her a primary challenge, will face Bobby Bright -- a former Democratic congressman who is now running as a Republican -- in the head-to-head matchup on July 17.
Roby fell short of 50% in part because she is paying a political price in deep-red Alabama for saying in 2016 that she would not vote for Trump.
"I cannot look my children in the eye and justify a vote for a man who promotes and boasts about sexually assaulting women," she said at the time.
If Roby were to lose the runoff, she would be the second House Republican defeated in a 2018 primary. Rep. Robert Pittenger of North Carolina lost to former pastor Mark Harris in May.
Smooth sailing for New Jersey Democrats
Two hotbeds of competitive House races held their primaries Tuesday. And while California had Democrats sweating, New Jersey went exactly according to plan.
Every candidate backed by the Democratic Congressional Campaign Committee and preferred by the party establishment claimed victory. In GOP Rep. Leonard Lance's district, former assistant secretary of state Tom Malinowski held off a progressive opponent. In retiring Republican Rep. Rodney Frelinghuysen's district, former Navy pilot Mikie Sherrill -- one of the strongest Democratic recruits of the 2018 cycle -- cruised.
And in retiring GOP Rep. Frank LoBiondo's district, state Sen. Jeff Van Drew -- whose conservative positions made him a target of progressives -- coasted.
The Democrat who faced a surprisingly close race Tuesday was Sen. Bob Menendez. Now free of corruption charges, Menendez' underfunded and unknown challenger Lisa McCormick put up a surprisingly strong showing. It was a clear sign that a strong challenger might have been able to unseat Menendez.
Democrats hope anti-Trump fervor is brewing in Missouri
Democrats, in response to Trump's presidency, have flipped a sizeable 42 state legislative seats since the President took office in January 2017, the latest of which came in Missouri on Tuesday night.
Democrat Lauren Arthur, a state representative, led Republican Kevin Corlew, also a state representative, by close to 20% with all precincts reporting. The swing is significant given the district in suburban Kansas City backed both Trump in 2016 and Mitt Romney in 2012. Additionally, the Republican who stepped down from the seat earlier this year won reelection in 2016 by over 20 percentage points.
Why does this small seat in Missouri matter nationally? Democratic operatives hope the swing previews a strong showing in November, where voters are prepared to rebuke the President.
But there are also statewide implications at play, too. Tuesday's special election was the first time voters have gone to the polls in Missouri since Republican Gov. Eric Greitens resigned in disgrace amid a series of scandals. The fact that voters rebuked the Republican in this race could be a bad sign for Missouri Attorney General Josh Hawley, who is seeking to oust vulnerable Democratic Sen. Claire McCaskill in November.
This story has been updated to reflect election results.