U.S. Rep. Christian Menefee holds a narrow lead over longtime Rep. Al Green in Tuesday's Democratic primary for Houston's 18th Congressional District, but possibly not avoiding a runoff, per preliminary votes. The big picture: If no candidate clears 50%, the race will head to a runoff — setting up a showdown between Menefee and Green. For Green, who was first elected in 2004, the stakes are steep after he decided to run in the 18th District when lawmakers redrew his old seat to tilt Republican. It also highlights the generational battles among older and younger members of the party. Menefee...