- Voters in seven states — Colorado, Maryland, Mississippi, New York, Oklahoma, South Carolina and Utah — will choose nominees for midterm races in their primary elections Tuesday.
- New York is the most closely watched state, as House primary elections there will set the stage for some of November's most important battleground seats.
- South Carolina voters will also decide if they want to re-elect a governor whom President Trump has repeatedly tried to boost.
House primary clashes throughout New York headline elections taking place Tuesday in seven states.
In addition to New York state, voters in Colorado, Maryland, Mississippi, Oklahoma, South Carolina and Utah will choose nominees for numerous races that will help to shape November's battle for control of Congress. Mississippi and South Carolina will hold runoffs for some primaries that were not settled in elections earlier this month.
New York voters will set the field for several battleground House races, which in November will help to determine whether Democrats can flip the 23 GOP-held seats needed to take a majority in the chamber. Primary voters will also choose the candidates in competitive House districts in Colorado in Utah.
President Donald Trump rallied in South Carolina on Monday night for ally Gov. Henry McMaster, who faces a GOP primary runoff.
Here are the biggest races to watch on Tuesday:
— New York graphic by CNBC's John Schoen
Former GOP Rep. Michael Grimm hopes to take back New York's 11th District, a Staten Island seat and the only one in New York City held by a Republican. The ex-representative, who served seven months in prison after he pleaded guilty to tax evasion in 2014, is challenging Republican Rep. Dan Donovan.
The bitter race has major stakes for November. Nonpartisan election analysts say the district leans Republican, but it could become more competitive in the general election in Grimm prevails.
Trump cited Grimm's potential November weakness in endorsing Donovan late last month. Donovan "will win for the Republicans in November...and his opponent will not," the president tweeted at the time. Cook Political Report's Partisan Voter Index, which gauges how districts vote in presidential elections relative to the country as a whole, rates it an "R+3" district.
The incumbent Donovan has easily raised more money than Grimm and had about $400,000 more on hand as of early June. The Democratic Congressional Campaign Committee has put its weight behind Army veteran Max Rose, the leading candidate to take on the GOP winner.
Elsewhere in the nation's largest city, one of the House's top Democrats faces an unexpectedly strong challenge. Rep. Joe Crowley will try to emerge victorious Tuesday in his blue 14th District, situated in Queens and part of the Bronx. Alexandria Ocasio-Cortez, a 28-year-old education advocate and community organizer, hopes to take down a representative who has served for nearly two decades.
Ocasio-Cortez has run to the left of Crowley. She has promoted proposals such as Medicare for all and a jobs guarantee, as well as her lack of corporate donors. Still, Crowley had more than $1 million on hand in early June, about 10 times more than Ocasio-Cortez.
The challenger has argued that Crowley — a 56-year-old white man — cannot properly connect with the diverse district.
While incumbents are generally favored, a challenger's victory would be a shake-up in both the 11th and 14th Districts. Some such as Trump predict a Grimm victory will make the Staten Island election more competitive in November. A win by Ocasio-Cortez would all but guarantee she would replace Crowley in Congress.
North of New York City, Democrats will choose challengers in two districts expected to be highly competitive in November. Nonpartisan handicappers consider both the 19th and 22nd Districts toss-ups in November.
A crowded field of at least five Democrats vies to take on GOP Rep. John Faso in November in the 19th District, which includes the Catskills and parts of the Hudson Valley. The seat is considered "R+2," according to Cook.
A few leading Democratic contenders have emerged. Lawyer Antonio Delgado has led the money race among Democrats, with more than $750,000 on hand as of early June. Businessman Brian Flynn and Army veteran Pat Ryan each raised more than $1.5 million by early June, but both had less money on hand than Delgado.
In the 22nd District, DCCC-backed education advocate Anthony Brindisi will run unopposed and will take on GOP Rep. Claudia Tenney. The seat, which stretches vertically from Binghamton in the south well into the central part of the state, is an "R+6" area, according to Cook.
Two other GOP-held districts in New York are considered competitive, but not as close as other seats in the state. In the 1st District on the eastern part of Long Island, GOP Rep. Lee Zeldin hopes to comfortably hold off a Democratic challenge. Businessman Perry Gershon has easily raised the most money among Democratic primary candidates, with a boost from his own pockets.
Democrats also aim to take out GOP Rep. John Katko in the 24th District. The central New York seat, which includes Syracuse, has flipped between parties frequently in recent elections.
The DCCC is supporting former prosecutor Juanita Perez Williams in a two-way Democratic primary. She runs against Dana Balter, a former special education teacher and advocate.
Trump swooped into South Carolina on Monday night to boost an ally. McMaster is one of numerous candidates this year that the president will try to boost with his influence.
A loss could cast doubts on the pull of Trump, who has repeatedly endorsed the governor.
He faces a Republican primary runoff Tuesday against businessman John Warren. In a five-way primary earlier this month, McMaster garnered about 42 percent of the vote, while Warren got about 28 percent.
Trump rallied in the state Monday ostensibly to support the governor's candidacy. Trump ended up addressing a wide range of topics in a freewheeling rally.
In a tweet Tuesday morning, the president said McMaster "is tough on Crime and Borders, loves our Military and our Vets and has created many jobs and a great economy."
Trump tweet: It was great being with Governor Henry McMaster last night in South Carolina. Henry is tough on Crime and Borders, loves our Military and our Vets and has created many jobs and a great economy. GO OUT AND VOTE FOR HENRY TODAY, HE WILL NEVER LET YOU DOWN!
In Colorado’s 6th District, Republican Rep. Mike Coffman hopes to defend his seat in November. The area just east of Denver has a “D+2” lean, according to Cook, making it a top target for Democrats.
On the Democratic side, Army veteran Jason Crow and former Obama administration Energy Department advisor Levi Tillemann aim to challenge Coffman. Crow has easily raised more money than Tillemann and has the DCCC's support.
Former GOP presidential nominee Mitt Romney aims to win the Senate seat in Utah vacated by Sen. Orrin Hatch's decision not to run for re-election. He faces a Republican primary against state Rep. Mike Kennedy.
Romney is widely popular in the state and expected to win comfortably. He has had to balance the desire to criticize some of Trump's policies — such as the separation of migrant children from parents — with his support of some policies such as the GOP tax law.
Salt Lake City Councilwoman Jenny Wilson is running unopposed on the Democratic side.
Only one Utah House race is expected to be competitive in November. GOP Rep. Mia Love's 4th District is considered one that "leans" Republican, according to nonpartisan handicappers. The central Utah area south of Salt Lake City is considered an "R+13" district, according to Cook.
Among Democrats, Salt Lake City Mayor Ben McAdams has led the fundraising race and has the DCCC's backing.
In Maryland, a crowded field of Democrats will vie to take on Republican Gov. Larry Hogan.
Several Democrats, including former Army private Chelsea Manning, are challenging Sen. Ben Cardin in Tuesday's primary. Manning is famous for her conviction for leaking top-secret government files.
Democrats in Mississippi will choose the challenger to Republican Sen. Roger Wicker.
Oklahoma Republicans will pick a new nominee for governor. Incumbent GOP Gov. Mary Fallin could not seek re-election because of term limits.