President Joe Biden’s border chief says he can’t explain why hundreds of thousands of migrants are rushing over the border he is tasked to guard. “Can you explain why you’ve seen this big surge [of migrants] in the last couple of weeks?” border chief Alejandro Mayorkas was asked on Friday, just six days before he lifts the Title 42 border barrier. “It’s very difficult to identify the cause,” the pro-migration border chief responded to the reporter.