“Some people say, well, given the hundreds of millions of dollars she raises it’s a small amount,” he said. “That’s true. But, that does not mean to say that the lobbyists thought she was a pretty good bet on this issue.”

It’s a classic Sanders attack, focusing on the appearance of soft corruption. And Clinton has accepted about $3 million in donations from lobbyists associated only with the fossil-fuel industry (though that’s a smaller number than the Sanders camp has claimed). According to an NPR fact check, employees in the oil and gas industry have donated $300,000 to Clinton’s campaign. By comparison, they’ve donated more than $1 million to Ted Cruz, about $50,000 to Sanders, and less than $10,000 to Donald Trump.

But later in the exchange, Sanders was able to tie the appearance of corruption to a specific policy, asking: “Are you in favor of a tax on carbon so that we can transit away from fossil fuel to energy efficiency and sustainable energy at the level and speed we need to do?”

Clinton, who does not support a carbon tax, didn’t answer directly. He pressed her again, and she still didn’t answer—though the moderators cut them both off. Her opposition is somewhat confusing. Carbon taxes are considered by many economists to be the ideal small-c conservative response to climate change: They price in global warming’s externalities, while allowing the market to choose how to divert resources elsewhere. (For her part, Clinton says she supported dropping subsidies for the oil industry while she was secretary of state.)

But when they got to what energy policy should include beyond a carbon tax, things got more muddled.

As secretary of state, Clinton pushed to expand hydraulic-fracture mining for natural gas (“fracking”) around the world; now, she wants to limit its use, but not ban it outright. Sanders, meanwhile, opposes fracking in all its forms. NY1’s Errol Louis asked Clinton why she changed her view.

“No, well, I don’t think I’ve changed my view,” she answered, saying she has always seen natural gas as a “bridge” between dirty-burning coal and clean, renewable energy. She added that expanding the use of fracking worldwide helped the United States strategically, as it decreased Russia’s ability to sell oil and gas to countries in Eastern Europe.

Though Clinton was at pains to make it look like her views haven’t changed, she could have just said that the expert understanding of fracking has changed. When drilling was new, many environmentalists supported it. There’s a good reason for that: Fracking has reduced U.S. carbon emissions by six percent this decade, devastated the coal industry, and changed the global economics of energy. And though fracking can have horrifying local environmental consequences, they do not seem to be nearly as widespread as initially feared. (In 2008, solar and wind power also just weren’t efficient enough as technologies to generate the electricity they can now.)