Talk about the pot calling the kettle black. The latest leak of emails from the Democratic National Committee ought, if nothing else, to put paid to the idea that Donald Trump has been playing to base instincts more than Secretary of State Clinton. The exchange between the chief financial officer of the DNC, Brad Marshall, and the committee’s chief executive, Amy Dacey, manages to disparage Jews, atheists, and Southern Baptists, all in a fell swoop.

And expose the DNC as biased against Senator Sanders. “It might may no difference,” writes Mr. Marshall, “but for KY and WVA can we get someone to ask his belief. Does he believe in a God. He had skated on saying he has a Jewish heritage. I think I read he is an atheist. This could make several points difference with my peeps.” Then he sends a second email by way of explanation: “It’s these Jesus thing.” Ms. Dacey writes back, in capital letters: “AMEN.”

Mr. Marshall has been quoted as suggesting he was referring in the exchange to someone other than Mr. Sanders, but no one will believe him. It’s all too typical of the cynicism that infects the whole Democratic operation, and it strikes us as newsworthy at a time when the Democrats are falling all over themselves to accuse Donald Trump and his camarilla of all sorts of bigotry against Mexicans, Muslims, and Jews, among others.

Senator Sanders is up in arms, of course; he’s been arguing all along that the DNC had rigged its operation. Of what these emails provide a glimpse is the nastiness with which the deck was stacked. And it suggests that the logical thing for Mr. Sanders to do is re-think whether it is to Mrs. Clinton that he wants to throw his endorsement. Whatever else one can say about Donald Trump, after all, he has made clear that he would welcome the Sanders voters.

He’s made a shout out to them at almost every opportunity, including at the convention in Cleveland. He’s the only one in the presidential race who’s actually attempting to run a big tent, welcoming all comers campaign. He may not have done it with a flair equal to, say, Ronald Reagan — but who has? Reagan’s big tent Republicanism helped him carry 46 of the 50 states in the 1980 election. Mr. Trump doesn’t have to do that well to win this election.