A State Senate runoff on Saturday in the Fort Worth suburbs will preview whether a backlash against conservative social policies will give Democrats a chance to gain.

An unusually competitive primary March 3 is driving early money, flood of ads, outside involvement and heavy voter outreach.

Texas voters have until Feb. 2 to register for the March 3 primary, which includes major statewide and El Paso races and multiple ways to sign up.

A special runoff election is being held Saturday to fill the vacant U.S. House seat in Texas' 18th Congressional District. Houston-area voters will decide between Democrats Christian Menefee and Amanda Edwards.