Although the spearphishing attempt in Florida had first been brought to light nearly two years ago when The Intercept cited a secret National Security Agency report, state officials said they were certain no elections computers had been compromised. The Mueller report turned that assertion on its head. “The F.B.I.,” it said, “believes that this operation enabled the G.R.U. to gain access to the network of at least one Florida county government.”

In an interview on Friday, Senator Marco Rubio of Florida took it one step further, saying that Russian hackers not only accessed a Florida voting system, but were “in a position” to change voter roll data.

The report has sent Florida officials scurrying once again for specifics. Which county? Could there have been more than one?

“They won’t tell us which county it was. Are you kidding me?” an exasperated Ron DeSantis, Florida’s Republican governor, said at a news conference in Miami on Thursday. “Why would you have not said something immediately?”