AUSTIN, Texas (AP) — As a budget shortfall in Texas threatens cuts to colleges and Medicaid, a costly border security operation is proving largely untouchable despite President Donald Trump's promises to build a wall and the plunging number of people caught illegally entering the U.S.

A prolonged oil slump has left lawmakers about $6 billion short of the money needed to keep the status quo in Texas, which attracts about a million new residents every two years. But border security is one area where Republicans — who control state government — have all but refused to search for savings.

During a...