After tens of thousands of migrant families, most from Central America, crossed the Rio Grande into Texas last summer, the government poured millions of dollars into two large detention centers meant to hold women and children — and keep more from coming.

But as U.S. Immigration and Customs Enforcement expands the centers to make space for the next wave of arrivals, the agency faces legal and political challenges that could shut them down. And a new flow of migrants raises questions as to whether the strategy has deterred migration at all.

One center is a purpose-built, 50-acre campus in Dilley, an hour’s drive southwest of San Antonio. Another, smaller center is tucked among derricks in Karnes City. They will be able to house some 3,400 migrants once they reach full capacity, just a fraction of those crossing, leaving ICE with few options besides releasing many with notices to appear in court, as it did in the past.

Some 130 House Democrats and 33 senators have called on the government to halt family detention, while a federal judge in California has tentatively ruled that the policy violates parts of an 18-year-old court settlement that says immigrant children cannot be held in secure facilities. ICE responded by pledging to improve its centers while it awaits the judge’s ruling.