Hillary Clinton and Bernie Sanders had an argument about financial regulation during Tuesday’s debate — but it wasn’t about whether to crack down on banks. Instead, it was about whose plan was tougher. The contrast with Republicans like Jeb Bush or Marco Rubio, who have pledged to reverse even the moderate financial reforms enacted in 2010, couldn’t be stronger.

For what it’s worth, Mrs. Clinton had the better case. Mr. Sanders has been focused on restoring Glass-Steagall, the rule that separated deposit-taking banks from riskier wheeling and dealing. And repealing Glass-Steagall was indeed a mistake. But it’s not what caused the financial crisis, which arose instead from “shadow banks” like Lehman Brothers, which don’t take deposits but can nonetheless wreak havoc when they fail. Mrs. Clinton has laid out a plan to rein in shadow banks; so far, Mr. Sanders hasn’t.

But is Mrs. Clinton’s promise to take a tough line on the financial industry credible? Or would she, once in the White House, return to the finance-friendly, deregulatory policies of the 1990s?

Well, if Wall Street’s attitude and its political giving are any indication, financiers themselves believe that any Democrat, Mrs. Clinton very much included, would be serious about policing their industry’s excesses. And that’s why they’re doing all they can to elect a Republican.