Primary voters head to the polls Tuesday in North Carolina, Indiana and Ohio, marking the first contests in a long series of contentious Republican battles over the next month.

In North Carolina, state Speaker Thom Tillis, Dr. Greg Brannon, and Pastor Mark Harris are vying for the GOP nomination to challenge Sen. Kay Hagan, D-N.C., in a marquee race that will help determine which party controls the Senate next year.

Further down the ballot, an American Idol runner-up hopes he’ll have better luck in a Tar Heel State House race and longtime Rep. Walter B. Jones, R-N.C., will try to avoid becoming the first incumbent to lose a primary this cycle. In Ohio, a spirited challenger — perhaps best known for parodying a Cialis commercial in his bid — will attempt to unseat Speaker John A. Boehner.

In North Carolina, the contests could drag out for months. Primaries for Senate, the 6th and 12th Districts might continue to a runoff on July 15 if no candidate receives at least 40 percent of the vote.

Here are six things to watch in those races and others on Tuesday:

1. Does the establishment get their guy now, or in two months?

National Republicans have pulled out all the stops to help Tillis win the nomination outright. Crossroads spent $1.6 million last month to boost him; the U.S. Chamber of Commerce put $764,000 behind ads supporting Tillis in the final two weeks of the primary. Jeb Bush and Mitt Romney endorsed him in the final week.

Barring some dramatic event, Tillis will get the most votes Tuesday. The question is whether he can reach the 40 percent threshold to avoid a runoff with Harris or Brannon. North Carolina political observers expect he will , but it is not a sure bet. If he does not win outright, Tillis has to spend two more months fighting a member of his own party, and Hagan gets extra time to define her opponent before he can.

2. Which 2016 hopeful wins the proxy battle?
All three of the major candidates in the North Carolina Senate race have been endorsed by Republicans openly mulling 2016 presidential bids: former Florida Gov. Jeb Bush backed Tillis, former Arkansas Gov. Mike Huckabee supported Harris, and Sen. Rand Paul, R-Ky., endorsed Brannon.

Of course, none of their presidential ambitions will be destroyed because they backed a losing candidate in a Senate primary. But the results are an indicator of their influence — especially for Paul, who made a last minute trip to the Tar Heel State on Monday to boost Brannon. If Harris beats Brannon for second place, that doesn’t look great for Paul. But if Brannon makes the runoff and spends the next two months bashing Tillis, Paul could get blame if Tillis — who will likely emerge victorious in a runoff — is weakened from those attacks before the general election.

3. What is Boehner’s Margin of Victory?

Boehner faced one of the most spirited primaries of his recent career this cycle. Three Republicans, including teacher J.D. Winteregg, ran against Boehner in this southwestern Ohio district. A Winteregg television spot — which parodied an erectile dysfunction ad for the drug company Cialis — went viral, delivering some national media attention to his bid (and ultimately cost Winteregg his job).

There’s no love lost between Boehner and some of the outside tea party groups — one of which spent more than $350,000 against his re-election. Republican operatives say Boehner is in little danger of losing his primary, which is tantamount to the general election in this conservative House district.

4. Does Jones Survive His Primary?

Jones faces the toughest primary of his 20-year career on Tuesday from Taylor Griffin, a former aide to President George W. Bush. Outside groups spent hundreds of thousands to attack Jones’ “liberal” record and boost Griffin — whose views align with the mainstream group of the Republican Party.

Despite this, North Carolina Republicans still said they expect Jones to win his primary.

5. Will Clay Aiken be a runner-up again?
The “American Idol” runner-up faces former North Carolina Commerce Secretary Keith Crisco and mental health counselor Toni Morris in the Democratic primary in this heavily Republican district. All three are vying to take on GOP Rep. Renee Ellmers in November.

Democrats in the district say Crisco has run a better primary campaign. Aiken’s fundraising was largely a disappointment, and initial start-up costs hindered him from using a large chunk of what he raised to convince voters to take his congressional aspirations seriously. And after being outspent on the air by nearly a 4 to 1 margin, Aiken’s team was forced last week to manage expectations for his prospects.

Whoever wins the Democratic nomination on Tuesday has long odds to oust Ellmers in this district, which voted for 2012 GOP presidential nominee Mitt Romney with 58 percent.

6. Which House Contests Head to Runoffs?
The GOP primary to replace retiring Rep. Howard Coble, R-N.C., turned nasty in the two-week run-up to the election — and the negativity might not end on Tuesday. International banker Bruce VonCannon went negative in an ad attacking the judicial record of Rockingham District Attorney Phil Berger Jr., the front-runner in the contest.

A recent internal poll showed Berger close to reaching the 40 percent threshold to avoid a runoff in the 6th District. But GOP operatives say the late-in-the-game negative campaigning only increased the potential for a runoff. Republican operatives described Baptist Pastor Mark Walker as the sleeper candidate. VonCannon and Greensboro City Councilmember Zack Matheny are also in the mix to advance.

In the adjacent 12th District, a crowded Democratic field is looking to replace Rep. Melvin Watt, who left the seat to lead the Federal Housing Finance Agency. State Rep. Alma Adams is the front-runner in that field. EMILY’s List recently boosted her campaign with mailers blanketing Democratic primary voters in the district. Democratic operatives say Adams could avoid a runoff out of the five-candidate field (one candidate dropped out in the weeks leading up to the primary). However if she doesn’t reach that 40 percent mark, Democratic operatives say state Sen. Malcolm Graham is a good bet to make the runoff.

Polls close at 7 p.m. in Indiana, where there are no competitive congressional primaries on Tuesday, and at 7:30 p.m. in North Carolina and Ohio.