(CNN) Tuesday's primaries in Connecticut, Minnesota, Vermont and Wisconsin set up some of the most crucial races in November's midterm election .

Voters in Wisconsin -- who were critical to President Donald Trump's 2016 victory -- will signal tonight if they are sticking with him or beginning to look for another option on who represents them in their state and in Washington.

Stay up to date on key election dates and other events, such as town halls and debates, as they get added throughout the year. Subscribe on your Google or Apple calendar.

Democrats are on the offensive in the Badger State, hoping to nominate a candidate to finally defeat Governor Scott Walker (R) and prove that Wisconsin's 2016 vote for Trump did not signal a permanent rightward shift for the state. Republicans are seeking to offset likely losses in Vermont and Connecticut by defending and flipping governor's mansions in those historically blue states, respectively.

In Minnesota, both Democrats and Republicans are targeting House races to flip, with those contests taking shape on Tuesday.

What we'll learn tonight

HOW STRONG IS DEMOCRATIC ENTHUSIASM IN THE MIDWEST? The Democrats' much ballyhooed "Blue Wall" crumbled spectacularly in 2016 as Pennsylvania, Michigan and Wisconsin all turned red, with Minnesota nearly following suit. Tuesday's races in Minnesota and Wisconsin will give an indication of just how high Democratic enthusiasm is going into 2018 and if the party can successfully defend its seats even in Trump territory. The states have reported strong early voting and absentee numbers. Will this be part of a possible "wave" in November?

HISTORY IN THE MAKING? Vermont Democrats appear poised to nominate Christine Hallquist for governor. She would be the first transgender major party gubernatorial nominee in US history but faces a tough campaign against popular Gov. Phil Scott, who is widely expected to win the GOP nomination. Hallquist adds to the record number of LGBT candidates running for office this year. Virginia Democratic state Rep. Danica Roem, who became the first out transgender candidate to win a state legislative seat in America last year, campaigned for Hallquist in the Green Mountain State.

IS MINNESOTA ABOUT TO TURN NOT SO NICE? An open governor seat, both Senate seats and a handful of competitive House seats could signal the campaign is about to heat up in the Land of 10,000 Lakes. President Trump endorsed Republican Pete Stauber in the 8th District's GOP primary to fill the open seat left by Democratic Rep. Rick Nolan. The President and Republicans know they need to stem the tide in the liberal bastion of Minnesota to avoid handing the speaker's gavel to Democrats. How Democrats coalesce around their nominees tonight will demonstrate the strength they have heading into November.

What to watch

Connecticut (Polls close 8 p.m. ET) - Retiring Democratic Gov. Dan Malloy's deep unpopularity in this state have Republicans eyeing the Connecticut gubernatorial race as a potential pickup during an otherwise tough election cycle.

Malloy chose not to seek reelection even though he was not term limited. Running to replace him on the Democratic ticket are businessman Ned Lamont and Bridgeport Mayor Joe Ganim. Lamont, who has been endorsed by the state Democratic party, rose to political fame in 2006 after besting then-Senator Joe Lieberman in the Democratic primary, and then losing to Lieberman in that year's general after the senator ran as an Independent. Ganim too has made a name for himself. The six-term mayor spent seven years in federal prison after being convicted of corruption charges in 2003.

The winner of that contest will face one of five Republicans: Danbury mayor Mark Boughton, who received the endorsement of the state Republican Party, former Trumbull First Selectman Tim Herbst, and businessmen David Stemerman, Bob Stefanowski, and Steve Obsitnik.

The race is expected to be highly competitive in November.

Vermont (Polls close 7 p.m. ET) - Vermont is one of two states where governors serve two-year terms rather than the more common four.

Republican Phil Scott, who first won election in 2016, will face voters again this November. Scott outperformed President Trump in Vermont by 22 points in 2016, enjoys sky-high approval ratings in the state and is the heavy favorite going into November.

On the Democratic side, former energy executive Christine Hallquist, activists Brenda Siegel and James Ehlers, and 14-year-old Ethan Sonneborn are vying for their party's nod.

If nominated, Hallquist would make history as the first transgender major-party gubernatorial nominee in America. On the Senate side, incumbent Bernie Sanders, an independent who caucuses with the Democratic party, will likely win and then decline that party's nomination. Sanders will then run (and most likely win) as an independent in the general election.

Minnesota (Polls close 9 p.m. ET) - Democratic Sen. Al Franken's resignation in January puts both of Minnesota's Senate seats on the ballot this year. Democratic Sen. Tina Smith, who was appointed to fill Franken's seat, is running for her party's nomination against Republican-turned-Democrat Richard Painter, a former White House ethics lawyer under President George W. Bush. She's been bolstered by a motivated party, increased support for female candidates and a Senate record that has impressed constituents during her short tenure. She could also be buoyed by incumbent Democratic Sen. Amy Klobuchar, whose popularity in the state has her on some lists as a potential 2020 candidate. Smith and Klobuchar are expected to face state Sen. Karin Housley and state Rep. Jim Newberger, respectively, but are widely expected to win in November.

The open governor's race is heavily contested on the Democratic side between US Rep. Tim Walz, state attorney general Lori Swanson, and state Rep. Erin Murphy. That race has been soiled by recent reporting that Swanson improperly directed her office's staffers to conduct political work for her campaign. The winner will likely face former Republican governor Tim Pawlenty, in what is expected to be a competitive race. Pawlenty is hoping his reputation supersedes any anger Democrats and Independents have towards the GOP.

The race to be Minnesota's attorney general was roiled days before the primary on Tuesday, when Rep. Keith Ellison was accused on Saturday of abusing an ex-girlfriend. He has denied the accusations, which were initially posted on Facebook by the woman's son.

Three of Ellison's opponents in the race -- state party-endorsed Minneapolis attorney Matt Pelikan, former Ramsey County attorney Tom Foley, and state Rep. Debra Hilstrom -- have all called upon Ellison to more thoroughly address the allegations.

In the House, both parties have a lot at stake. CNN currently ranks five of the state's eight districts as competitive. Democrats think they can win some of the 23 seats needed to regain control of the House, but Republicans are excited about their candidate in MN-08, former pro hockey player and police officer Pete Stauber, for whom Trump held an election rally in June. In MN-01, the state party endorsed Jim Hagedorn, who narrowly lost the seat to Walz in 2016. Hagedorn first must beat conservative state Sen. Carla Nelson, who has attracted support from the NRA and megadonors Richard Uihlein and Paul Singer. The winner will face likely Democratic nominee Dan Feehan, a veteran and former acting Assistant Secretary of Defense under President Barack Obama.

Wisconsin (Polls close 9 p.m. ET) - Republican Governor Scott Walker is a political survivor - he famously won three statewide gubernatorial elections in four years and is the only governor in US history to win a recall election. He acknowledges 2018 will be his toughest test yet, but it's still unclear which Democrat he'll face.

Democrats are split on who they think could beat Walker. Wisconsin public instruction superintendent Tony Evers has led in the limited available public polling, but firefighter and union president Mahlon Mitchell was endorsed by popular Democratic Sen. Kamala Harris.

Democratic Sen. Kirsten Gillibrand and progressive group EMILY's List stepped in to support former state assembly member Kelda Roys, while Madison mayor Paul Soglin represents a stronghold of Wisconsin Democrats and could siphon support from the frontrunners in his city.

A recent NBC/Marist poll showed Evers with 25% support and none of his competitors above 7%, though nearly half of voters remained undecided less than a month before the election. That same poll showed Evers with a substantial lead over incumbent Walker, 54% to 41%.

On the Senate side, two Republicans are vying for the opportunity to challenge incumbent Democratic Sen. Tammy Baldwin. Either State Senator Leah Vukmir, who has the support of the Wisconsin Republican establishment, or veteran Kevin Nicholson, once a rising star in the Democratic Party before he commenced an ideological about-face, will face an uphill battle against Baldwin's massive cash advantage and leads against both in head-to-head polling.