But Mr. Stone insisted in an interview that the contact had been brief and involved nothing more than the exchange of a few direct messages, well after the party committee had been hacked. “Even if he is a Russian agent, my cursory exchange with him happens after he releases the D.N.C. stuff,” Mr. Stone said on Saturday. “There’s only one exchange with him. I had no further exchanges.”

Mr. Stone said the exchange took place after he had published an article on Aug. 5 on the Breitbart News site about the hacking, which the American government has tied to a Russian effort to meddle in the election. After Guccifer 2.0 had been suspended by Twitter, Mr. Stone posted a message against “censorship” and then had what he called an “innocuous” exchange over direct message.

“You would need a time machine in order to collude, and, as I said yesterday, Putin has not yet perfected a time machine,” he said, referring to the Russian president, Vladimir V. Putin.