Over the past few weeks, a quiet legal crisis has been unfolding on the US-Mexico border. Texas has seized control of part of the border and claimed the right to prevent federal authorities from exercising jurisdiction there. After the US supreme court ruled that the federal government could tear down razor wire erected by Texas authorities, the state vowed to erect more – and Governor Greg Abbott claimed that because the federal government had failed to protect his state from an “invasion” of refugees, it has “broken the compact between the United States and the States” and lost the right...