Border policy covers physical barriers, personnel, surveillance, and the processing of people who arrive seeking asylum. Enforcement capacity and legal obligations interact, and changes in one produce pressure on the other.
Encounters at the southern border fluctuate with conditions in origin countries, economic demand, smuggling networks, and US policy signals. Attributing changes to any single cause is difficult.
US law and treaty commitments allow people physically present to apply for asylum regardless of how they entered. Adjudicating those claims takes years given immigration court backlogs, and that delay shapes behavior on all sides.
Most illicit fentanyl is seized at official ports of entry, frequently in vehicles driven by US citizens, which complicates arguments that link drug interdiction primarily to unauthorized crossings between ports.