With two weeks remaining before the May 6th primary, the North Carolina FreeEnterprise Foundation wants to highlight the NC Senate races where an incumbent state senator is facing a challenge from within their own party.

Among current state senators running for re-election, there are four Democrats and five Republicans facing a primary opponent. Of these, our analysis and local intelligence shows four bear keeping an eye on going into the home stretch:

Senate District 3 (Bertie, Chowan, Edgecombe, Hertford, Martin, Northampton, Tyrrell and Washington), where incumbent Sen. Clark Jenkins faces two opponents, Northampton County Board of Education member Erica Smith-Ingram, and Baptist preacher Alan Mizelle from Bertie County.

This district has a NCFEF Conventional Voter Behavior (CVB) rating of Strong Democratic, with 71.5% Democratic voter registration and 54.6% of voters African American - it went 61.9% for President Obama in 2012. There is no Republican on the ballot, so the winner of the Democratic Primary is the winner in the fall.

Jenkins won a primary challenge handily with 67% of the vote against a single challenger in 2012, but had a closer race in the last midterm, winning 50% against two opponents in 2010. 

From Edgecombe (home to 31.7% of district voters) and able to provide significant personal resources to his campaign, Jenkins does face the challenge inherent in a low voter turnout three-way Democratic Primary in a majority minority district where two of the three candidates running are white (Jenkins and Mizelle).

Senate District 28 (part of Guilford) has incumbent Sen. Gladys Robinson facing Skip Alston, a realtor and former chair of the Guilford County Board of Commissioners, as well as past president of the NC Chapter of the NAACP.

Robinson slipped onto the ballot in 2010 following the then-incumbent Katie Dorsett's decision to withdraw from the race just two weeks after filing to run, causing some locally to contend a behind-the-scenes deal had been struck between the two.

Guilford County Commissioner Bruce Davis unsuccessfully challenged Robinson in both 2010 and 2012, but is running this year in the Democratic primary in the 6th Congressional district.

Alston has strong ties within the Greensboro real estate and business community, and started the race with a healthy $25,000 cash-on-hand, compared to Robinson's $8,200. Conversations with local folks recently revealed a sense Alston is making a strong case he would be more aligned on business and economic issues than Robinson, who had a score of 24.4 on the 2013 NCFEF Legislative Business Ratings.

Senate Districts 33 (Davidson and Montgomery) and Senate District 36 (Cabarrus and part of Union) find Republican incumbents Sen. Stan Bingham and Sen. Fletcher Hartsell each facing a single primary rival: Bingham faces Republican Party activist and business owner Eddie Gallimore in District 33, and Hartsell faces former Cabarrus County Clerk of Court and attorney Fred Biggers in District 36. 

Both districts are NCFEF CVB rated as Strong Republican, with Mitt Romney and Pat McCrory each receiving over 60% of the vote in 2012. There's no Democrat running in either district, so the Republican Primary determines the winner in each.

For these two, it appears that local political dispositions are at the heart of the challenge.

In 2012, Bingham barely cleared the 40% threshold needed to avoid a runoff in a Republican primary that featured Gallimore and another Republican, but this time Bingham faces Gallimore in a one-on-one matchup. As he did last election, Gallimore has consistently criticized Bingham for not being as conservative as the voters of the district.

Hartsell ran unopposed in 2012, but comes into this election cycle having faced campaign finance allegations in 2013. Hartsell has also been highly vocal against the Alcoa position relative to its owning and operating four hydro-elective dams in the area, an issue that is emotionally charged for both sides locally.

In these two districts, it will be the hotly contested US Senate Republican primary driving overall voter turnout - a greater concentration of Tea Party and social conservatives among Republican primary voters could present a significant challenge for these two Republican incumbents.

There are other districts where incumbents face challengers, but at this point it doesn't appear the primary is competitive:

Senate District 5 - Democrat Sen. Don Davis faces former state senator Tony Moore and Henry Williams II.

Senate District 21 - Democrat Sen. Ben Clark faces three challengers, educator Sylvia Adamczyk, activist and perennial candidate Eronomy Smith, and Cumberland County Commissioner Billy King.

Senate District 31 - appointed incumbent Republican Sen. Joyce Krawiec faces realtor Steve Wiles and local business owner Dempsey Brewer. The Republican nominee will face Democrat attorney John Motsinger in the fall.

Senate District 39 - Republican Sen. Bob Rucho faces trial attorney Matt Arnold.

Senate District 47 - Republican Ralph Hise faces McDowell County Commissioner Michael Lavener.

Next, NC House primary races to watch.