Mueller’s Office Will Grill Him About Roger Stone. He Will Respond With Comedy.

“I got to stay sober until Sept. 7,” Mr. Credico said. “You know what I mean? That’s my day. Because if I start I won’t stop. I don’t want to go in there all wacked out, inarticulate, mumbling and all of that. The last year has been very difficult.”

Mr. Credico said he has been given the O.K. by the special counsel’s team to bring his dog, Bianca, a fluffy 14-pound Coton de Tulear, to the grand jury proceedings, and is considering doing so.

Bianca has accompanied him to media appearances, and is yet another point of contention with Mr. Stone, who once taunted Mr. Credico by threatening to take Bianca; Mr. Stone now says he was only concerned about the dog’s health.

Mr. Credico called Bianca a therapy dog.

“If I have her with me, I definitely can’t take her to a bar,” he said, adding, “She’ll protect me from my demons.”

He was on his game during a 90-minute interview, running through impressions of Jackie Mason, George W. Bush, Mr. Sharpton, Mr. Koch, Strom Thurmond and Ronald Reagan. His Giuliani, in which he retracts his head, froglike, into hunched shoulders, is particularly adept.

If nothing else, the grand jury will not be in for the usual fare.

“I can’t even begin to imagine,” Mr. DiNapoli, the state comptroller, said. “One would wish there would be livestreaming of that.”

Mr. Credico’s lawyer, Martin Stolar, said, “It’s a serious investigation and Randy is obligated to tell the truth, and that’s what he’s going to do.”

But he conceded impressions were not off the table.

“You know Randy,” he said. “He’s not entirely controllable.”