Understandably, her critics are having a field day. But here’s the real question: What in heaven’s name can she say? That the crisis at the border is of Mr. Biden’s own making, created by a slew of grandstanding executive orders issued right after he was sworn into office, which would-be migrants took as a green light to come on in? That the administration still has no comprehensive policy to address the problem, even as the White House knows his handling of the issue is his weakest polling point with the American people? That Mr. Biden needlessly ended the “Remain in Mexico” policy for asylum seekers simply because Donald Trump had been for it? That given all this, any sane vice president surely recognizes the political reality that any visit to the border will quickly become a national gotcha moment? Yes, vice presidents are often assigned the tough sells. It’s also true that a President Harris would likely have done the same thing Mr. Biden did. But “root causes,” to which Ms. Harris turns whenever she’s asked about the border, is what you say when you know that what you’re doing isn’t going to work, the implication being that it really can’t be fixed at all.