So now, in a last desperate attempt to beat the arithmetic, the Sanders campaign is turning the implicit character attack explicit, and doing so on the weakest possible ground. Clinton, who has said that coal is on its way out, is a tool of the fossil-fuel industry because some people who work in that industry gave her money? Wow.

Sanders himself got to play the issue-oriented purist, in effect taking a free ride on other peoples’ character defamation. There was plenty of nastiness from Sanders supporters, but the candidate himself seemed to stay above the fray.

But Mr. Sanders, hunched over a U-shaped conference table, rejected it as a personal attack on Mrs. Clinton’s income — the sort of character assault he has long opposed. She has the right to make money, he offered.