Rep. Monica De La Cruz (R-TX) is facing a challenge from House candidate Ada Cuellar as the Democratic Party seeks to flip her South Texas district blue.

Cuellar, a Harlingen-based emergency physician, on Thursday became the first Democrat to launch a campaign seeking to oust De La Cruz from her seat representing the state’s 15th Congressional District, which lies in Hidalgo, one of the most populous counties in the Rio Grande Valley.