The dispute centers on the regulation of so-called “shadow banks”—large institutions like AIG, Lehman Brothers, and Bear Stearns who were not subject to the same rules as big commercial banks that take deposits. The collapse of all three firms precipitated the free-fall that led to a $700 billion bank bailout passed by Congress. In a lengthy financial-reform plan Clinton unveiled in October, she called for strengthening regulations and reporting requirements on these companies to lessen the risk of another “too-big-to-fail”-type economic spiral. And as Sanders prepared to detail his own proposals on Clinton’s home turf Tuesday, her campaign launched an unusual pre-emptive attack by releasing an aggressive statement from her chief financial officer, Gary Gensler, a former top regulator at the Commodity Futures Trading Commission.

Unfortunately, Senator Sanders has so far taken a hands-off approach to some of the riskiest institutions and activities in our economy, which were among the biggest culprits during the 2008 crisis. In his speech tomorrow, Senator Sanders should go beyond his existing plans for reforming Wall Street and endorse Hillary Clinton’s tough, comprehensive proposals to rein in risky behavior within the shadow banking sector.

Gensler’s missive got the attention of Sanders, who devoted a big chunk of his speech on Tuesday to rebutting the Clinton campaign’s argument.

Now, my opponent, Secretary Clinton says that Glass-Steagall would not have prevented the financial crisis because shadow banks like AIG and Lehman Brothers, not big commercial banks, were the real culprits. Secretary Clinton is wrong. Shadow banks did gamble recklessly, but where did that money come from? It came from the federally-insured bank deposits of big commercial banks—something that would have been banned under the Glass-Steagall Act.

Sanders said that as president, he would immediately order his Treasury secretary to draw up a list of firms—both traditional banks and “shadow banks”—that were too big to fail. Within a year, he said he would use provisions under the Dodd-Frank law to break them up, necessitating a vote only of regulators, not Congress. (Whether that is even possible is a matter of debate, as Quartz notes.)

If Sanders plans to break up large “shadow banks,” does that mean they don’t need the additional regulations and reporting requirements that Clinton is proposing? His campaign won’t say, but Sanders’s policy director, Warren Gunnels, told me that Gensler’s suggestion that Sanders was taking a “hands-off” approach to the firms was “absurd.” The new Glass-Steagall Act that Sanders supports, he said, “would strike at the heart of shadow banking” because it would prohibit those firms from getting their financing from commercial banks.

“It really doesn’t make any sense to me that they would say that,” Gunnels told me Wednesday in a phone interview. “It’s really disingenuous to make the claim that Senator Sanders is somehow not concerned about shadow banking. Of course he’s concerned about shadow banking.” Gunnels also took a passing shot at Clinton’s messenger and his Wall Street ties. “Senator Sanders doesn’t take his advice from a former Goldman Sachs executive who supported the repeal of Glass-Steagall during the Clinton administration,” he said of Gensler.