2018 Election: Results in Ohio; primary results in Kansas, Michigan, Missouri, Washington

Voters in four states – Kansas, Michigan, Missouri and Washington – went to the polls Tuesday to determine party nominees ahead of November's midterms. There was also a closely watched special election in Ohio to fill the vacancy left by the resignation of Republican incumbent Rep. Pat Tiberi.

Here are four takeaways from Tuesday's elections:

• Democrats fought Republicans to an effective tie in Ohio's 12th Congressional District, an ordinarily safe Republican seat that has only been represented by a Democrat once since 1939. Republican Troy Balderson has a narrow lead over Democrat Danny O'Connor, but as of Wednesday morning the major news networks and the Associated Press say the race remains too close to call.

• If Trump-endorsed gubernatorial candidate Kris Kobach wins the Republican primary in Kansas over incumbent Jeff Colyer, it could help Democrats steal control of the statehouse in November. As of Wednesday morning, Kobach held a narrow lead with most of highly populated Johnson County left to be counted.

• In a big victory for labor unions, Missouri voters soundly rejected a new law that would have allowed non-union members to opt out of paying union dues even if they benefit from collective bargaining.

• In Michigan, former state Rep. Rashida Tlaib is likely to become the first Muslim woman elected to Congress after winning the primary to fill the seat vacated by Democratic Rep. John Conyers Jr., who was forced to resign over sexual harassment allegations.

The most important race of the evening was a special election that took place in Ohio's 12th Congressional District, where Democrats still hold out hope they can steal a congressional seat Republicans have safely held for more than 20 years (since 1939, the district has only been represented by a Democrat for one term). In fact, outgoing Republican incumbent Rep. Pat Tiberi won the district by about 37 percentage points in 2016.

As of Wednesday morning, Republican Troy Balderson held a narrow lead over Democrat Danny O'Connor. The Associated Press, CNN and NBC News all said the race remained too close to call, mostly due to 5,048 absentee ballots and 3,435 provisional ballots that have yet to be counted.

In the wake of stunning defeats in both Pennsylvania and Alabama, an effective tie in a safe Republican district is yet another sign that a Democratic blue wave could crash down on Washington in November. "This district is ruby red Republican. The fact that it is so close is a big deal," CNN chief national correspondent John King said during the network's live coverage Tuesday night.

>> READ MORE: Poll: Conor Lamb leads Keith Rothfus big, Dem enthusiasm high in key Pa. congressional race

Despite the outstanding ballots, Trump took credit for Balderson's apparent victory late Tuesday night, claiming his last-minute rally in the district on Saturday pushed Balderson over the finish line. Pre-election polling, however, does not support Trump's claim, indicating the race was headed to a neck and neck finish.

Trump shook up what should have been an easy primary win for incumbent Republican Gov. Jeff Colyer with his endorsement of far-right challenger Kris Kobach. As of Wednesday morning, the race remained too close to call.

Kobach holds a narrow lead over Colyer, but Johnson County in the suburbs of Kansas City has yet to full report its results. If Kobach wins the nomination, it could offer Democrats the rare chance to win a statewide race in deeply conservative Kansas. The ultimate Republican winner will face State Sen. Laura Kelly, who won the Democratic nomination against former state Rep. Josh Svaty and former Wichita mayor Carl Brewer.

A Kobach victory in Tuesday's Republican primary could also seriously impact the races for two congressional seats Democrats hope to flip in November.

In the Second Congressional District, Democrat Paul Davis will face Republican Steve Watkins, who won a seven-man Republican primary that insiders fear won't yield a candidate popular enough to win in November. Davis, the former minority leader in the Kansas House, nearly defeated former Gov. Sam Brownback in 2014.

In the Third Congressional District, which Democrats held as recently as 2011,  attorney and former MMA fighter Sharice Davids narrowly defeated Bernie Sanders-backed Bret Welder for the Democratic nomination. If she defeats Republican opponent Kevin Yoder in November, Davids would become the first Native American woman elected to Congress.

In the Wolverine State, Democrats are eying an opportunity to flip another statehouse, thanks to the retirement of unpopular incumbent Republican Gov. Rick Snyder.

For the Democrats, former minority leader Gretchen Whitmer won the Democratic primary over progressive opponent Abdul El-Sayed. She will now face off against Attorney General Bill Schuette, who was endorsed by Trump and defeated Lt. Gov. Brian Calley in Tuesday's Republican primary.

"The reality is, this is President Trump's Republican party. His chosen candidates win Republican primaries," Calley said in a concession video Tuesday night.

Democrats also see an opportunity to flip two Congressional districts that are considered toss-ups.

In the Eighth Congressional District, Democrats are pinning their general election hopes on former CIA officer Elissa Slotkin, who served on the National Security Council under presidents George W. Bush and Barack Obama. Slotkin, who coasted to an easy Democratic primary win Tuesday night, will face off against incumbent Republican Rep. Mike Bishop in a district Trump won by less than 7 points in 2016.

Another toss-up is the 11th Congressional District, which was a free-for-fall with a total of 10 candidates thanks to the retirement of Republican Rep. David Trott. Both party's races remained too close to call Wednesday morning. On the Republican side, the frontrunners were former Rep. Kerry Bentivolio, state Sen. Mike Kowall and state Rep. Klint Kesto. For the Democrats, there's Sunell Gupta, the brother of CNN host Sanjay Gupta; former Obama official Haley Stevens and Fayrouz Saad, who has the endorsement of progressive Alexandria Ocasio-Cortez, an upset Democratic primary winner for Congress in New York.

In the 13th Congressional District, where incumbent Rep. John Conyers Jr. was forced to resign over sexual harassment allegations, former state Rep. Rashida Tlaib is likely to become the first Muslim woman elected to Congress after edging out Detroit City Council President Brenda Jones in the Democratic primary. Tlaib will not face a Republican opponent in November in the heavily Democratic district, but could end up seeing token opposition from a write-in candidate.

Among the most interesting races in November will be Democratic Sen. Claire McCaskill's attempt to defend her seat in a state Trump won by more than 18 percentage points. McCaskill easily won the Democratic primary, and will face state Attorney General Josh Hawley in the fall.

The Second Congressional District is also expected to be somewhat competitive in the fall. Attorney Cort Vanostran won the Democratic primary Tuesday night, and will face off off against three-term Republican incumbent Rep. Ann Wagner in November.

In a big victory for labor unions, Missouri voters soundly rejected a new law that would have allowed non-union members to opt out of paying union dues even if they benefit from collective bargaining. Proposition A, as the referendum was known, was the first opportunity for voters to weigh in following an important Supreme Court ruling from June impacting public sector labor unions.

>> READ MORE: How the Supreme Court ruling on labor unions in Janus vs. AFSCME could upend politics in Pennsylvania

Washington's primary is similar to California's, where the top two primary finishers regardless of political party move on to November's election. Former state Republican chair Susan Hutchinson emerged from a scrum of 28 candidates to challenge incumbent Democratic Sen. Maria Cantwell, who is seeking her fourth term in the U.S. Senate and is the overwhelming favorite.

As far as congressional seats are concerned, Democrats have a good chance to flip at least two Republican-controlled districts come November.

In the Fifth Congressional District, Republican incumbent Rep. Cathy McMorris Rodgers will face Democratic nominee Lisa Brown, the former chancellor of Washington State University Spokane.

Democrats have a shot to flip the Eighth Congressional District, which is being vacated by retiring incumbent Republican Rep. Dave Reichert. Democrats were locked in a competitive primary fight for the right to face Republican Dino Rossi. The Democratic frontrunners are all first-time candidates: pediatrician Kim Schrier, doctor Shannon Hader and attorney Jason Rittereiser. The race remained too close to call Wednesday morning.