North Carolina

When: May 6


Major Candidates: State House Majority Leader Thom Tillis, physician Greg Brannon, pastor Mark Harris

Why it matters: Perhaps no primary has been as active as early as the Tar Heel State's GOP contest. Already Brannon, backed by Sen. Rand Paul of Kentucky, and Harris are accusing the establishment-backed Tillis of being a squishy moderate. Tillis's fundraising with Karl Rove suggest he isn't hiding the fact he's the Republican Party's candidate-of-choice, either. The incumbent Democrat, Sen. Kay Hagan, is vulnerable, but North Carolina's purple tint means Republicans don't have a free pass for her seat. Even if Tillis wins, he risks stretching himself too far to the right to win the primary.

Georgia

When: May 20

Major candidates: Reps. Jack Kingston, Phil Gingrey, Paul Broun, former state Secretary of State Karen Handel, businessman David Perdue

Why it matters: It's the Democrats' favorite primary. The free-for-all field is seen as near-certain to move to a summertime runoff between the top two finishers. And if Broun or Gingrey fill either spot, the GOP is in trouble. Both, but especially Broun, have a history of incendiary rhetoric that would give Democrats a chance to win this New South red state. Their presumptive nominee, Michelle Nunn, has the famous father and fundraising chops to be an ideal standard-bearer, even if she is new to politics.

A competitive Peach State race in the fall would be a major blow to the GOP's hopes of retaking the Senate. Watch to see if Republican power brokers can discreetly knock Broun and Gingrey out of the way.

Iowa

When: June 3

Major candidates: State Sen. Joni Ernst, talk-radio host Sam Clovis, businessman Mark Jacobs, former U.S. Attorney Matt Whitaker

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