AUSTIN, Texas — Sen. Rand Paul (R-KY), in an exclusive interview with Breitbart News here at the South By Southwest music and art festival, says former Secretary of State Hillary Clinton “clearly broke the law” by using a private email system. That makes him the first major Republican and potential challenger of hers to say so.

“I think she clearly broke the law,” Paul, a likely 2016 GOP presidential candidate, said.

In fact, she fired one of her ambassadors for not using government email. I think people don’t like hypocrisy. She also has said she did it for convenience because she didn’t want to have two phones—but of course within days she had admitted that she does have two phones. I think convenience, which is her excuse at this point—to carry just one phone—I think that convenience should never trump national security. I think when she says, “oh I never transmitted classified information” the problem is is that her schedule is classified. She’s going to tell us she never got her schedule emailed to her? The reason it’s classified is to protect her whereabouts. We wouldn’t want enemies to know where our Secretary of State is at all times. But she also doesn’t just put herself at risk by sending these messages on an unsecured server, she also puts at risk the people who defend her and the people who are responsible for her safety if that schedule were to get out to people who want to harm the Secretary of State.

Paul added that it’s unfathomable that no communications Clinton had on the private email address and server were classified—because, among other reasons, she was communicating via email with President Barack Obama himself.

“The other possibility is that I think hasn’t been clearly explained yet is she says ‘well I didn’t ever push send and send classified information,’” Paul said.

If you want to as a journalist use the Freedom of Information Act to get the conversations between the president and the Secretary of State, what do you think the response is going to be? Most of these conversations are classified. So that’s the thing, she’s going to say she communicated with the president by email but she’s going to assure us that’s not classified? She’s also going to say “I did obey the law here, trust me I went through and I only discarded the things that were non-governmental.” I think this goes to judgment—or her lack of judgment. It’s kind of what I’ve been saying all along about how I think her poor judgment with regard to Benghazi should preclude her [from being president]. This is just another example I think of really poor judgment I think when she is sort of placing herself above the law.

Nonetheless, despite the fact Paul says she broke the law, he doesn’t think it will be easy to hold her accountable because she’ll try to use her influence to get off.

“I think she’ll stonewall and she’ll stonewall and she’ll try to prevent any release of any of the emails, but I think there needs to be an independent investigation,” Paul said.