AUSTIN, Texas (AP) — Democrats are salivating at the prospect of flipping a wealthy Houston enclave that has been solidly Republican since sending George H.W. Bush to Congress in 1967 — the kind of race they'll have to win for any hope of retaking the House in the November midterms.

But first that means navigating a potentially bruising intraparty primary that underscores the lingering rift from the 2016 Democratic presidential contest, a showdown between Bernie Sanders' progressive wing and the Hillary Clinton establishment. Corporate attorney Lizzie Pannill Fletcher is facing off against act...