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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 be in March. What to watch for as the primaries begin:

Some 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, 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 Fifth 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. 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 in the first test for a Bannon-backed Senate challenger.

Two key Senate primaries 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 state Sen. Kevin de Leon in a “jungle” primary, in which the top two contenders advance to the general election regardless of party. In Minnesota’s Eighth District, former FBI counterterrorism analyst Leah Phifer is challenging Rep. Rick Nolan for the DFL endorsement. Both candidates have said they will abide by the endorsement process.

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 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.

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 tossup race according to the political newsletter Inside Elections with Nathan L. Gonzales. Democratic primaries in Texas’ Seventh 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 Second 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.

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

Two open seat primaries to watch are tossup races in Minnesota’s First District and New Hampshire’s First 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.

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