Fracking, particularly as a means of drilling for fossil fuel, was a controversial topic of discussion during Tuesday night’s presidential debate between Donald Trump and Vice President Kamala Harris. Harris’ comments on the subject have rubbed some viewers the wrong way, and Trump has been steadfast in his efforts to increase drilling and production capacity in the U.S.

Not exactly sure what fracking is, and why Harris’ stance on the topic is under fire? Let’s take a look:

What is fracking?

According to NBC Chicago, fracking, also known as “hydraulic fracturing,” is a process that involves breaking apart shale rock with pressurized liquid made from water and other chemicals. The resulting cracks help fossil fuels like natural gas and petroleum to flow freer than usual, the BBC reported.

Why is fracking controversial?

Fracking has several harmful causes, including tremors in the Earth’s surface and its use of massive quantities of water, which also needs to be transported to the appropriate location. Per NBC Chicago, researchers at Yale found the practice to be a colossal waste of water, and found a connection between the release of several dangerous greenhouse gases like methane into the atmosphere.

Pro-fracking individuals say the U.S. needs to use the practice more as a means to reduce the country’s reliance on other countries. Organizations like the American Petroleum Institute note that thousands of jobs connected to the energy sector (both directly and indirectly) depend on practices like fracking.

What’s Harris’ stance on fracking?

In 2020, leading to primaries, Harris said on more than one occasion that she supports banning the practice to help address climate change and related environmental issues.

“There’s no question I’m in favor of banning fracking, and starting with what we can do on day one around public lands,” she told CNN during a climate change town hall in 2019, according to NBC Chicago. Now, Harris’ stance has changed, per the Associated Press.  

In an interview with CNN, Harris talked about her reasons behind her changed position, and shared that she voted to expand fracking leases as vice president.

Trump took the opportunity to call her out on the topic, and other shifts in policy stances she’s made.

“She gave up at least 12 and probably 14 or 15 different policies,” he said, per to NBC Chicago.