Trucks inched through traffic and some stores reported fewer customers in U.S.-Mexico border towns on Wednesday as staffing shortages tied to a surge in asylum seekers slowed checkpoints and threats of the border closing scared away shoppers.

U.S. President Donald Trump reiterated his threat to close the border, or parts of it, saying Congress could avert such a shutdown by changing laws to fix what he called immigration "loopholes."

Business leaders on both sides of the border have lashed out against the threat, saying a shutdown would hurt supply chains and $1.7 billion in daily trade at some of the world's busiest land crossings.