Primary voters in four more states — Connecticut, Wisconsin, Minnesota and Vermont — go to the polls on Tuesday.

This year's been dominated by talk of Democratic gains, but today Republicans will pick nominees in several places where they hope to flip House seats and even governors' mansions.

Two Republicans who failed to win the White House are hoping voters will elect them to lead their states for a third time — but one's trying to make a political comeback after almost a decade out of office.

We'll find out who could replace House Speaker Paul Ryan in his Wisconsin district.

And Vermont Democrats could make history by nominating a transgender woman for governor.

Here's a rundown of the important contests to watch in each state:

Democrats have been aiming to take out Republican Gov. Scott Walker for years now, including in a failed 2012 recall attempt. But with winds blowing more favorably their way this year, and as Walker seeks a third term, his numbers have dropped in the state ever since his failed 2016 presidential bid. Democrats hope this could be the year, even in a state that President Trump carried two years ago.

But Democrats have a crowded eight-way contest to settle first. Wisconsin Superintendent of Schools Tony Evers had led in most public polls, arguing he's successfully won statewide before. Former state Rep. Kelda Roys has had impressive fundraising. She could benefit in a year boosting Democrat women, and she's gotten the endorsement of EMILY's List and New York Sen. Kirsten Gillibrand. Mahlon Mitchell, president of the state's Professional Firefighters Association, would be the state's first black governor if elected. He's gotten support from the state SEIU and AFL-CIO, as well as California Sen. Kamala Harris.

Republicans are challenging Sen. Tammy Baldwin here as well, in one of 10 states that Trump carried with Democratic Senators up for reelection, though it's not one of the most competitive contests. State Sen. Leah Vukmir and Marine Corps veteran Kevin Nicholson are in a close fight, with both arguing they're the best conservative choice. Vukmir has gotten more of the GOP establishment support, with endorsements from Speaker Ryan, the Wisconsin GOP and the NRA. Nicholson has the backing of The Club for Growth and FreedomWorks. Vukmir has attacked Nicholson for his past as a Democrat, while Nicholson has criticized Vukmir for her past criticism of Trump during the 2016 presidential primary.

Ryan's retirement in the 1st Congressional District leaves an open seat that Democrats had already hoped to compete for, even before the House speaker decided not to run again. Ironworker Randy Bryce generated a lot of buzz last year with his announcement video that went viral. That helped him raise more than $6 million and get the endorsement of the Democratic Congressional Campaign Committee. But his primary opponent, teacher and Janesville School Board member Cathy Myers, has criticized him for multiple past arrests, including a DUI, and his delinquency on child support payments. On the GOP side, businessman Bryan Steil is the favorite and has been endorsed by Ryan. Also still on the ballot, though, is Paul Nehlen, an alt-right activist and white nationalist who was banned by Twitter for racist tweets.

There are primary fights on both sides in the open gubernatorial contest. Former Republican Gov. Tim Pawlenty is trying to make a political comeback, but 2014 GOP nominee Jeff Johnson is arguing his time is past. Johnson got the endorsement of the state Republican Party after Pawlenty decided not to seek their blessing, but the former governor has the hefty fundraising lead.

The Democratic side is a five-way race, with ideological divides on full display. Polls show former Rep. Tim Walz and Attorney General Lori Swanson in the lead. State Rep. Erin Murphy got the endorsement of the state's Democratic-Farmer-Labor Party, outgoing Gov. Mark Dayton and key unions in the state. She's criticized both Swanson and Walz for their past "A" ratings from the NRA, but both candidates say their views have now changed on gun control.

Democratic Sen. Tina Smith, the state's former lieutenant governor who was appointed to the seat after Sen. Al Franken resigned amid allegations of sexual misconduct, is trying to win her primary for a full term. She's the favorite against several candidates, the most notable of which is former George W. Bush ethics lawyer Richard Painter, a vocal Trump critic who decided to switch parties to run for the Senate. The DFL has accused him of being an opportunist.

Rep. Keith Ellison, the deputy chairman of the Democratic National Committee, is running for state attorney general against four other candidates. But his campaign has been beset in the final stretch by allegations of domestic abuse by an ex-girlfriend. Ellison, a progressive leader and first Muslim elected to Congress who's been outspoken in support of the #MeToo movement, has denied the allegations.

Minnesota's congressional races also offer ripe pick-up opportunities for both parties. Republicans are eyeing open seats in Walz's 1st District and the 8th District, where Democratic Rep. Rick Nolan is running for lieutenant governor, as both Democratic districts voted for Trump by double digits in 2016. Incumbent Democratic Rep. Collin Peterson's 7th District did too, but since he is running again it may be a harder seat for the GOP to flip.

Democrats have targets in the Twin Cities suburbs — freshman GOP Rep. Jason Lewis in the 2nd District and Republican Rep. Erik Paulsen in the 3rd District, which Hillary Clinton won by almost 10 points in 2016.

Republicans have rare opportunities for gains in this typically blue state. Democratic Gov. Dannel Malloy decided not to run again, saddled with falling approval ratings amid a state budget crisis. Now, the GOP hopes that could give them an opening in the gubernatorial race. Danbury Mayor Mark Boughton has been endorsed by the state Republican Party. Wealthy businessmen Bob Stefanowski and David Stemerman have put a lot of their own money into the race.

The Democratic race is between Ned Lamont, who defeated then-Sen. Joe Lieberman in the 2006 Democratic primary, only to lose to him in the general after the incumbent successfully ran as an independent. Bridgeport Mayor Joe Ganim is also running, but he's got baggage after serving seven years in federal prison on corruption charges.

The 5th Congressional District is open since Democratic Rep. Elizabeth Esty announced she wouldn't run again after mishandling allegations of abuse within her staff. This is a district that Hillary Clinton only carried by four points, so Republicans see a chance. The Connecticut GOP had endorsed former Meriden Mayor Manny Santos, while retired psychology professor Ruby Corby O'Neill and businessman Rich DuPont are also running.

Democrats will choose between Jahana Hayes, the 2016 National Teacher of the Year, and former local official Mary Glassman. Glassman has been endorsed by the state Democratic Party, while Hayes has progressive backing and supports a single-payer health care system. Hayes also has the backing of Sen. Chris Murphy, who recruited her to run for his old House seat, and Sen. Kamala Harris, both possible 2020 Democratic presidential candidates.

Sen. Bernie Sanders is up for reelection. He's likely to receive the nomination of the Vermont Democratic Party, but plans to decline it and run as an independent, even with Democrats' backing.

Democrats could have a chance to topple Republican Gov. Phil Scott, who saw his approval ratings tumble earlier this year after signing laws tightening state gun laws. They could also make history with their nominee. Christine Hallquist, a former electric company executive, would be the first transgender person nominated for governor by a major party if she wins.

There are several other candidates running too, including 14-year-old Ethan Sonneborn, who got on the ballot thanks to a quirk in a state law that doesn't set age requirements for candidates.

Sonneborn still can't vote for himself, though.

Copyright 2018 NPR. To see more, visit