Spread out over the first nine months of the year, primaries will set the stage for the 2018 midterm elections in November. These contests will be the first test of each party’s ability to field strong candidates in key pickup opportunities and fend off intraparty challenges. 

The first elections will take place in March. Here’s what to watch for as the primaries pick up. And click here for Roll Call’s comprehensive guide to every 2018 election from start to finish.

Taking on incumbents

Some primary candidates have opted to take on sitting lawmakers from their own parties. 

On the Republican side, President Donald Trump’s former adviser Steve Bannon has threatened to support primary challengers against Republican incumbents. The March filing deadlines will be key to watch, as challengers could emerge in Nebraska, Mississippi and Utah. Wyoming’s June deadline is another to keep on the radar.

With North Carolina’s primary scheduled for May 8, Rep. Robert Pittenger could be the first lawmaker to lose a contest. His primary challenger, former pastor Mark Harris, has reportedly caught Bannon’s attention. Harris lost a 2016 challenge to Pittenger by just 133 votes, and he outraised Pittenger in the most recent fundraising quarter. 

In Colorado’s 5th District, Rep. Doug Lamborn faces a handful of Republican challengers, including state Sen. Owen Hill and 2016 Senate candidate Darryl Glenn. Even before the June 26 primary, Lamborn could run into trouble. In order to get on the ballot, candidates have to either gather signatures by March 20 or receive at least 30 percent of the vote at a party assembly in April.

June and August will host a number of primaries should Senate challengers emerge. If state Sen. Chris McDaniel decides to challenge GOP Sen. Roger Wicker in Mississippi, they would face off on June 5, which would be the first test for a Bannon-backed Senate challenger.

Two key Senate primaries hosting intraparty battles are Nevada’s on June 12, with GOP Sen. Dean Heller facing perennial candidate Danny Tarkanian, and Arizona’s on Aug. 28, with Republicans competing for the GOP mantle in the open-seat race.

A few incumbent Democrats also have primary challengers. Sen. Dianne Feinstein of California will face Democratic state Sen. Kevin de León in a jungle primary, in which the top two contenders advance to the general election regardless of party. In Minnesota’s 8th District, former FB.I counterterrorism analyst Leah Phifer is challenging Rep. Rick Nolan for the Democratic-Farmer Labor endorsement. Both candidates have said they will abide by the endorsement process.

Senate challengers 

Senate Democrats are largely on defense this cycle, with 10 running in states Trump won. Multiple Republicans are vying for the nomination in some of those contests. 

We’ll have a better sense of the how the general election Senate contests will shape up starting in May, as Republican voters choose their candidates.

On May 8, Republicans will face off in West Virginia, Ohio and Indiana, three key states with hotly contested Senate races. Primaries for Montana and North Dakota will occur in June, while contests in Missouri and Wisconsin will occur in August. 

House and Senate Battlegrounds Taking Shape for 2018

Crowded fields

This cycle an unprecedented number of Democratic candidates are running for the House across the country.

The primaries will test many of the political newcomers and determine which candidates can run successful campaigns. Republicans are hoping nasty primary fights will drain resources and cause candidates to stake out positions that could be too liberal for the general election. 

Democrats will face their first tests in the early primaries in March, particularly in Texas on March 6.

The Texas primaries will determine which candidate will face GOP Rep. Will Hurd in the 23rd District, a Toss-up race according to Inside Elections with Nathan L. Gonzales. Democratic primaries in Texas’ 7th District, represented by GOP Rep. John Culberson, and the 32nd District, held by GOP Rep. Pete Sessions, are also crowded, even though those districts are more likely to stay Republican.

Another date to watch is June 12, when Democrats in Maine will pick their candidate. Democrats are targeting GOP Rep. Bruce Poliquin in the 2nd District.

There is also a potential June primary in Virginia’s 10th District, where a crowded field of Democrats are competing to take on GOP Rep. Barbara Comstock. Democratic presidential nominee Hillary Clinton carried the district by 10 points. There has been some discussion among district party officials of using an alternative method to select the candidate, like a convention. But if they do decide to go with a primary, it would be held on June 12.

Open seats

So far there are 30 open seats in 2018, thanks to lawmakers retiring or running for higher office. Inside Elections ranks nine of them as competitive. In these races, candidates will compete in both the Democratic and Republican primaries.

Two open seat primaries to watch are Toss-up races in Minnesota’s 1st District and New Hampshire’s 1st District. 

The Aug. 14 Minnesota primary could determine which candidates will look to fill the seat vacated by Democratic Rep. Tim Walz, who is running for governor. But the district parties typically endorse their favorites ahead of time, which could narrow the field before the primary election.

The contenders in the New Hampshire Toss-up race won’t be determined until the Sept. 11 primary.

Open seat primaries are also key in races that are solidly Democratic or Republican, since the winner of the favored party’s primary would likely become a member of Congress.

One date to watch in those solid contests is Aug. 2, which could determine three new Republican members of Congress.

There are three open seats in Tennessee, all Solid Republican according to Inside Elections: the 2nd, vacated by retiring Rep. John J. Duncan Jr.; the 6th, vacated by Rep. Diane Black, who is running for governor; and the 7th, vacated by Rep. Marsha Blackburn, who is running for Senate.

As the elections kick off, keep track of all of the key primary contests and more campaign news with At the Races.

Simone Pathé and Inside Elections’ Leah Askarinam contributed to this report. Watch: Which Members of Congress Might Come Be Back in 2019?