- Four more states — Wisconsin, Minnesota, Connecticut and Vermont — will hold primary elections on Tuesday.
- In Minnesota, four House races will play a major role in determining which party holds the House after November's midterms.
- Wisconsin holds closely watched Senate and governor's races, as well as a contest for outgoing House Speaker Paul Ryan's seat.
Battles in Midwestern swing states headline another packed round of primary elections on Tuesday.
In Wisconsin, which voted for Trump in 2016, Republicans vie to challenge Democratic Sen. Tammy Baldwin in November. New faces will fight for outgoing House Speaker Paul Ryan's 1st District, and GOP Gov. Scott Walker will once again face a fight for his political life.
Voters in Minnesota will pick nominees for four competitive House races, two of which are perhaps the GOP's best chances to flip Democratic-held seats. The state is one of the major battlegrounds in the fight for control of the House after November's elections.
Here are some notable races to watch on Tuesday:
Baldwin is one of 10 Senate Democrats facing re-election this year in a state Trump carried two years ago. Still, she appears relatively safe. The president won her state by less than a percentage point.
Marine Corps veteran Kevin Nicholson and conservative activist and nurse Leah Vukmir are the leading candidates in Tuesday's Republican Senate primary. An NBC News/Marist poll last month found Baldwin had a double-digit lead over both possible challengers.
In the state's 1st District, Ryan's retirement puts his longtime seat on the competitive map. On the GOP side, former Ryan aide Bryan Steil is considered the front-runner and has received the House speaker's endorsement.
Both ironworker Randy Bryce and Janesville School Board member Cathy Myers have tried to leverage Democratic Party energy in a competitive primary. Bryce has been one of the fundraising juggernauts of the House cycle, taking in more than $6 million so far.
In Wisconsin's other notable statewide race, Walker seeks his third term. The governor, who survived a rare recall election in 2012, faces a difficult environment again this year.
Walker is favored to make it through the GOP primary on Tuesday. State schools Superintendent Tony Evers is the front-runner on the Democratic side.
An NBC News/Marist poll last month showed some possible weakness for Walker. It found a double-digit lead for Evers in the potential general election matchup.
Trump endorsed his 2016 campaign rival on Monday. In a tweet, he called Walker "a tremendous Governor who has done incredible things for that Great State."
While considerable attention has focused on how larger states such as California and Pennsylvania will affect Democrats' push to take a House majority, Minnesota also will also play a critical role. Nonpartisan election analysts rate two seats held by each major party as toss-ups in November.
The Democratic Party hopes to stop the GOP from flipping two of its seats in which an incumbent is not running. The current minority party needs to win 23 total GOP-held seats to take a House majority.
- 1st District: Democratic Rep. Tim Walz vacated the seat to run for governor. Former Department of Defense official Dan Feehan appears to lead the Democratic field to succeed him. In the Republican field, Jim Hagedorn — who had challenged Walz previously — vies for the nomination with state Sen. Carla Nelson on Tuesday.
- 2nd District: Democrat Angie Craig is running unopposed in her bid to challenge GOP Rep. Jason Lewis. The former executive at a medical device company lost to the Republican representative by about 2 percentage points in 2016. Craig has both raised and spent more money than Lewis in the race so far.
- 3rd District: Multiple Democratic candidates aim to challenge incumbent GOP Rep. Erik Paulsen in November. Democratic businessman Dean Phillips leads the fundraising race among his party's primary candidates and appears to have the edge in Tuesday's race.
- 8th District: Democratic Rep. Rick Nolan's retirement gives the GOP an opening to potentially flip the 8th District seat. Republican retired police officer Pete Stauber, who earned a Monday endorsement from Trump, is the front-runner in Tuesday's primary. State Rep. Jason Metsa and former state Rep. Joe Radinovich are among the candidates hoping to emerge from a crowded Democratic primary field on Tuesday.
Republicans have a chance to make some races interesting this year in traditionally blue Connecticut. Unpopular Democratic Gov. Dannel Malloy declined to run for re-election, and public opinion of him could potentially be a drag on the members of his party trying to succeed him.
Businessman Ned Lamont — who toppled then-Sen. Joe Lieberman in a Democratic primary in 2006 but lost in the general election as Lieberman mounted an independent bid — and Bridgeport Mayor Joe Ganim are among the candidates on the Democratic side. Republican contenders include Danbury Mayor Mark Boughton and businessman Bob Stefanowski.
A Democratic representative's decision not to run for re-election amid scandal has also made a House seat in Connecticut more competitive than usual. Democratic Rep. Elizabeth Esty will not seek another term after reports that she allowed an-ex chief of staff to continue serving after allegations that he harassed and threatened a female staffer.
Republicans plan to contest the seat, which leans Democratic. The state GOP has endorsed former Meriden Mayor Manny Santos in Tuesday's primary. Former local Democratic official Mary Glassman and teacher Jahana Hayes face off for the Democratic nomination.
Democratic Sen. Chris Murphy also faces re-election this year, although the largely popular lawmaker is expected to have few problems staying in office in November.
Democrats aim to challenge Republican Gov. Phil Scott in blue-leaning Vermont. Candidate Christine Hallquist, a former electric company executive, could make history Tuesday as the first transgender gubernatorial nominee for a major party.
Well-liked independent Sen. Bernie Sanders and Vermont's lone congressman, Democrat Peter Welch, are expected to breeze to re-election in November.