Foreign actors hacking into state election systems could still be a concern, according to the nation's top cyber official.

During a Senate hearing Tuesday, National Security Agency Director and U.S. Cyber Command head Adm. Michael Rogers said he thought there were "scenarios where you could see capability applied" to infiltrating the systems in certain geographic areas. Sen. John McCain, R-Ariz., had pressed him on whether it was plausible that Russian hackers could "somehow harm the electoral process" in McCain's home state; last month, the FBI issued an alert suggesting state voting systems could be targeted by cyberattacks.

But Rogers noted that the fact that states have separate voting systems could be an advantage.

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"The structure is so disparate, with some elements being still very manually focused, others being very electronically and interconnected," Rogers said during the hearing. "Because it's not just one nationwide single, integrated structure, that tends to help us ... defensively."

During the Senate Armed Forces Committee hearing, which touched on other topics including encryption, senators called for a more concrete plan outlining exactly how the Defense Department and other federal agencies would respond to future cyberattacks.

McCain said during remarks the country needs a draft plan about "what the United States' actions would be in the case of a threat, in the case of an actual attack."

“If you don’t act, I guarantee you Congress will act," McCain said during the hearing, addressing Rogers and Marcell Lettre, undersecretary of defense for intelligence.