Sen. Ron Wyden this week pledged to block a vote confirming Lt. Gen. Joshua Rudd as the new head of both U.S. Cyber Command and the National Security Agency, citing his lack of digital warfare and intelligence experience.

Rudd, who is currently the deputy chief at U.S. Indo-Pacific Command, has held several leadership posts throughout his military career, but he has no background in cyber operations or signals intelligence.

Despite his service, Rudd “does not have the background that would allow him to immediately step into” the role of leading Cyber Command, Wyden wrote in a letter that was included in the Congressional Record on Wednesday.

“He is not qualified for this job,” the Oregon Democrat added. “And, when it comes to the cybersecurity of this country, there is simply no time for on-the-job learning. The threat is just too urgent for that.”

In his first confirmation hearing, Rudd downplayed his lack of bona fides.

“For decades I have had the opportunity to be a leader, consumer, enabler, generator and integrator of the intelligence and operational capabilities of the NSA and Cyber Command,” he said.  “I’m confident that, if confirmed, I can continue to lead and enable those two organizations to provide the best support to our combat commanders in the joint force, writ large.”

Wyden, one of the Senate’s top privacy hawks, also wrote he opposed Rudd’s confirmation because of the vague answers he provided the Intelligence Committee in January about his understanding of the NSA’s surveillance authorities.

“I did everything in my power to allow him to demonstrate some understanding of the basic guardrails of NSA's authorities and got nothing but vague assurances about following the law.”

Wyden’s blockade means the Senate might need to hold a formal vote on Rudd’s nomination, instead of approving it by unanimous consent as has usually been done with picks to lead Cyber Command and NSA.

Both organizations have been without a permanent chief for nearly a year, ever since President Donald Trump fired former leader Gen. Timothy Haugh. Lt. Gen. William Hartman has been leading the command and the spy agency in an acting capacity.

While a lawmaker’s hold has traditionally meant uncertainty for a nominee, Senate Republicans last year deployed the "nuclear option" to alter the chamber’s rules in order to confirm Trump's picks faster. If Wyden continues to resist, Rudd could be included in such a package.

The Defense Department did not immediately respond to a request for comment.