WASHINGTON — Senate Armed Services Chairman John McCain said Tuesday he would block the separation of the National Security Agency from Cyber Command's "dual-hat" leadership if the White House were to attempt such a move.

At a committee hearing in which Adm. Michael Rogers, the head of both organizations, testified, McCain said he was "troubled" by reports that Defense Secretary Ash Carter and Director of National Intelligence James Clapper back a White House plan to separate the two. He ripped the administration for not informing Congress before the news appeared in the press.

If the two agencies are separated "prematurely," McCain R-Ariz., vowed to object to the nomination of any individual the president nominates to replace the director of the NSA if that person is not also nominated to be the commander of Cyber Command.

"I do not believe rushing to separate the dual hat in the final months of an administration is appropriate given the very serious challenges we face in cyberspace and the failure of this administration to develop an effective deterrence policy," he said.

McCain pointedly asked Rogers whether he stood by prior professional military advice, which was that "maintaining the dual hat is in our best national security interests," to which Rogers replied, "Yes."

Rogers reportedly told an audience at a security summit earlier this month that he favors separating the two while keeping them aligned.

McCain, in his opening statement, said the issue raises larger concerns about whether the Defense Department is appropriately organized to manage defensive and offense requirements of the cyber mission.

McCain, a frequent critic of the Obama administration on defense issues, faulted its technological agility and its "failure to confront deficiencies in cyber policy" as undermining DoD's ability to deter and respond to attacks.

Central to the hearing were reports that Arizona and Illinois have already experienced attempted hacks of their voter databases and the disclosure by US officials that they are expanding their investigation because other states may have been targeted. Officials have not publicly said yet who they suspect, but Russia is suspected to be responsible for a hack of the Democratic National Committee.

Facing a tough general election in his home state, McCain grilled Rogers and Undersecretary of Defense for Intelligence Marcel Lettre over the reports, asking how the US would respond. When Lettre demurred, pointing to the FBI's "aggressive" and ongoing investigation, McCain turned testy.

"I'm asking you if we have a policy [to respond] and the answer is, 'No,'" McCain said.

Later, asked if there are scenarios in which hackers could disrupt the voting results in Arizona, Rogers said there were. However, the disparate structure of the country's electoral system makes it easier to protect, he said.

McCain and lawmakers of both parties pressed Rogers and Lettre on the issue of a cyber deterrence policy. Lettre said new laws and regulations are not as valuable as giving the administration a free hand to collaborate with the private sector.

"I agree," McCain said. "Right now, there is no policy, no policy you can describe to me as to what we can do about an attack or pending attack. So there is a vacuum there, and if you don't act, Congress will act."

President Obama in July approved a presidential order laying out a framework for an interagency response to attacks on critical infrastructure, in which the Defense Department has a role.

"Do I have the capability to protect aspects of critical infrastructure? Yes, sir," Rogers said in one exchange.

That seemed to fuel questions from Sen. Richard Blumenthal, D-Conn., and McCain, about the response to the alleged tampering with the technology underpinning US elections.

"Wouldn't the selection of our leaders, our system of government [be considered critical infrastructure]," McCain said. "If you attack that, you succeed in destroying democracy. Why are we equivocating here?"'

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