Sen. Kamala Harris pressed Supreme Court nominee Brett Kavanaugh about whether he’d talked with anyone working with President Donald Trump’s lawyer about the Russia investigation.

In a tense exchange Wednesday, the California Democrat asked Kavanaugh if he had ever spoken with anyone at the law firm Kasowitz, Benson & Torres about Special Counsel Robert Mueller’s investigation into Russia’s interference in the 2016 U.S. presidential election. Marc Kasowitz, one of the firm’s partners, has long worked with Trump.

“Have you had any conversation about Robert Mueller or his investigation with anyone at that firm?” she asked.

Kavanaugh appeared confused by the question. He asked Harris: “Is there a person you’re talking about?”

The exchange between the two went on for a few minutes, as Harris, a former prosecutor, repeated her line of questioning and Kavanaugh said while he didn’t remember, he did not know everyone employed at the law firm. He never answered the question.

“I think you’re thinking of someone and you don’t want to tell us,” Harris said.

When asked about the exchange between Harris and Kavanaugh, a Democratic aide told TIME, “We have reason to believe that a conversation happened and are continuing to pursue it.”

Democrats have questioned Kavanaugh on how he would rule in matters related to Mueller’s probe. Asked this week if a sitting president would be required to respond to a subpoena, Kavanaugh declined to answer. He also did not answer a question about whether Trump has the right to pardon himself.

Get our Politics Newsletter. The headlines out of Washington never seem to slow. Subscribe to The D.C. Brief to make sense of what matters most. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Write to Mahita Gajanan at mahita.gajanan@time.com and Alana Abramson at Alana.Abramson@time.com.