U.S. officials think massive surge at southern border possible if Covid restriction is lifted Thursday

U.S. officials are quietly preparing for what they think could be the biggest surge in traffic at the southern border in decades if a Covid restriction that has blocked most migrants for almost two years is lifted Thursday.

On a call this week with senior Department of Homeland Security officials, Secretary Alejandro Mayorkas asked whether the department was prepared for a worst-case scenario in which 350,000 to 400,000 migrants cross the border in October, according to two DHS officials familiar with the conversation.

A number that high would nearly double the 21-year...