Both General Nakasone and Mr. Bolton, through spokesmen, declined to answer questions about the incursions into Russia’s grid. Officials at the National Security Council also declined to comment but said they had no national security concerns about the details of The New York Times’s reporting about the targeting of the Russian grid, perhaps an indication that some of the intrusions were intended to be noticed by the Russians.
Speaking on Tuesday at a conference sponsored by The Wall Street Journal, Mr. Bolton said: “We thought the response in cyberspace against electoral meddling was the highest priority last year, and so that’s what we focused on. But we’re now opening the aperture, broadening the areas we’re prepared to act in.”
He added, referring to nations targeted by American digital operations, “We will impose costs on you until you get the point.”
Administration officials said they believed Mr. Trump had not been briefed in any detail about the steps to place “implants” — software code that can be used for surveillance or attack — inside the Russian grid.
Pentagon and intelligence officials described broad hesitation to go into detail with Mr. Trump about operations against Russia for concern over his reaction — and the possibility that he might countermand it or discuss it with foreign officials, as he did in 2017 when he mentioned a sensitive operation in Syria to the Russian foreign minister.