CEDAR RAPIDS, Iowa — Senator Bernie Sanders of Vermont edged closer on Friday to directly attacking Hillary Rodham Clinton, pointedly asking whether the Democratic presidential front-runner would support measures to break up the country’s largest financial institutions and reinstate a firewall between commercial and investment banking.

Mr. Sanders, whose campaign for the Democratic presidential nomination has galvanized liberal activists driven by questions of economic fairness, highlighted his efforts to cut down the so-called too big to fail banks and restore Glass-Steagall, the Depression-era banking law repealed under President Bill Clinton. “You’ll have to ask Hillary Clinton about her views on whether she thinks we should break up these large financial institutions. I do,” Mr. Sanders, an independent, said at a news conference here. “You will have to ask her views on whether we should re-establish Glass-Steagall.”

He boasted that he had not received financial contributions from Goldman Sachs, which he said sought “undue influence” in American politics, but stopped short of calling on Mrs. Clinton to reject the nearly $50,000 in donations she has received from employees of the Wall Street firm. “That’s her decision,” Mr. Sanders said, after pausing for a moment to consider the question.