Sen. Rand Paul is holding up the confirmation of a key national security official over concerns about a government surveillance program, an administration official confirmed to The Daily Beast.

He has temporarily blocked John Demers –– currently Boeing’s assistant general counsel –– from being confirmed as Assistant Attorney General for the Justice Department’s powerful National Security Division, according to that source. Paul’s concern about Demers, per sources, is that he has vocally defended Section 702 surveillance, which lets the NSA collect electronic communications.

Paul’s office did not respond to multiple requests for comment on this story, though they did send out a press release on his “Special ‘Festivus’ Edition of ‘The Waste Report.’”

If confirmed, Demers will be one of just three DOJ officials with the power to sign off on Foreign Intelligence Surveillance Act (FISA) warrant applications. Those warrants let the FBI agents surveil U.S. citizens who they believe are agents of a foreign power.

And that work has drawn scrutiny from Republican political operatives in the wake of reports that Carter Page –– formerly a foreign policy adviser to President Donald Trump’s campaign –– and Paul Manafort were both the subjects of FISA warrants.

Though Demers is nominated to fill one of the administration’s most powerful and important national security positions, his confirmation process is coming unusually late in the president’s term. The Senate confirmed Barack Obama’s first nominee for the position, David Kris, just three months after his inauguration. Trump didn’t even announce he planned to nominate Demers until September of this year.

Paul’s hold on Demers’ confirmation likely means he won’t be confirmed for the position until at least a year into the Trump presidency. Dana Boente, the U.S. Attorney for the Eastern District of Virginia, currently holds the post.

A former official from the National Security Division told The Daily Beast that Demers has a reputation for being “unobjectionable and not particularly partisan,” and that people in the national security space were largely pleased and relieved that Trump nominated him for the influential post.

Rand Paul has long been one of the Senate’s most vocal critics of a spying program known as Section 702, part of the FISA Amendments Act. It lets the National Security Agency (NSA) collect electronic communications –– including emails –– to and from foreign targets. Demers helped draft the law, as the Washington Post noted. Its critics –– including Paul –– say it results in the bulk collection of emails Americans send to people outside the country, invading their privacy and undermining their Constitutional rights.

“We’ve got this massive database of warrantlessly collected communications that the FBI can sift through for purposes unrelated to terrorism or national security,” said Julian Sanchez, a senior fellow at the libertarian Cato Institute.

Its defenders say the program is vital to preventing terrorist attacks, and that it has many layers of safeguards and oversight to keep the FBI from misusing the collected emails. They also say its flexibility is necessary to surveil the global internet.

The legislation permitting Section 702 surveillance will expire on January 19. Members of Congress are currently working to find a way to renew it. And the debate cuts across partisan lines; many members of the conservative Freedom Caucus, libertarian-leaning Senate Republicans, and privacy-focused Democrats want the renewal of the legislation to change how the surveillance works. Defenders of the legislation say changes could make it less effective.

Josh Geltzer, formerly a lawyer in the front office of the National Security Division, told The Daily Beast that Demers, if confirmed, will be “a critical policy voice on wide-ranging national security issues.”

“I think it should be a top priority, especially with all that’s occurring in the national security space right now, to have someone senior and approved by the Senate filling such an important role,” he said.