Naomi Klein, the Canadian social justice activist and best-selling author, declared in a new interview that, when it comes to climate, she does not trust Hillary Clinton.

In an interview preview aired Tuesday, Klein argues that Clinton's corporate ties make her a "vulnerable" candidate for the presidency and that Democratic rival Bernie Sanders is a "significantly better candidate."

"I think that Bernie Sanders could win in a general election," Klein told Mehdi Hasan, host of Al Jazeera's "UpFront."

"The logic of her candidacy," Klein said, "was because she had so much money. A lot of it was just, 'she's unbeatable—look how deep the pockets are.'"

"I don't trust her because as secretary of state, when she had a huge megaphone to make this an issue, to show that she understands the connections between human security and climate, she didn't use the megaphone."

The "irony," Klein explains, is the sources of that money and "the entanglement of the Clinton Foundation, with so many corporations and so many governments," is precisely what makes her "vulnerable."

"So, on the one hand, it's what supposedly makes her inevitable. And on the other hand, it's what I think makes her a very weak candidate and makes Bernie Sanders a much better candidate," she said.

Watch the preview below. The full interview will air on Al Jazeera's "UpFront" program on Friday, March 18 at 3:30 pm EST.

Hasan asked Klein if, given Clinton's eleventh-hour opposition to the Keystone XL tar sands pipeline, would she trust the candidate on climate change as president. Klein, who authored This Changes Everything, which makes the case that capitalism is in direct conflict with environmentalism, replied: "I don't trust her on climate at all."

"I don't trust her because as secretary of state, when she had a huge megaphone to make this an issue, to show that she understands the connections between human security and climate, she didn't use the megaphone," Klein said. 

Finally, when forced to say if she would choose between Clinton and one of the Republican candidates, all of whom appear to be climate change deniers, Klein admits that she would support Clinton, adding, "but it would be extraordinary important if she does become the candidate to put a lot of pressure on her from the outside."