FISA program that helped take down Zawahiri is expiring. Officials are sounding the alarm.

Top U.S. officials on Tuesday began their formal efforts to sound an alarm to Congress on a surveillance program -- one they describe as "critical" to protecting national security -- that is set to expire at the end of this year.

The statute, Section 702 of the Foreign Intelligence Surveillance Act, lays the groundwork for the government to be able to collect the communications of non-Americans overseas who message on U.S.-based platforms without use of a warrant.

The program has drawn scrutiny, however, over the incidental collection of Americans' communications that are swept up in the process -- and the ability for officials at agencies to in certain cases search through that collected information.

"What keeps me up at night is thinking about what will happen if we fail to renew Section 702 of FISA," DOJ Assistant Attorney General Matt Olsen said in a speech at the Brookings Institution Tuesday. "In the 15 years since enactment, Section 702 has become the Intelligence Community’s most valuable national security legal tool. And we must retain it to confront the evolving threats we will be facing ahead."

Attorney General Merrick Garland and Director of National Intelligence Avril Haines sent a joint letter to congressional leaders Tuesday morning urging them to reauthorize the program, listing several specific instances in which Section 702 was used to disrupt national security threats.

Section 702-acquired information helped contribute to the successful U.S. targeting of al-Qaeda leader Ayman al-Zawahiri last year, has helped officials quickly identify foreign perpetrators of ransomware attacks against critical infrastructure inside the U.S., and helped authorities disrupt foreign adversaries' attempts to recruit spies in the U.S.; among other examples outlined by Garland and Haines.

President Joe Biden's national security adviser Jake Sullivan also expressed the administration's support for reauthorization of Section 702 in a statement this morning, describing the program as a "cornerstone of U.S. national security."

"This authority is an invaluable tool that continues to protect Americans every day and is crucial to ensuring that U.S. defense, intelligence, and law enforcement agencies can respond to threats from the People’s Republic of China, Russia, nefarious cyber actors, terrorists, and those who seek to harm our critical infrastructure," Sullivan said.

House Republicans, including Judiciary Committee Chairman Rep. Jim Jordan of Ohio, have already made clear their plans to fight any effort to reauthorize the program without significant concessions. In appearances on Fox News and other conservative outlets, they have sought to tie the issue to concerns voiced by former President Donald Trump and his long-running attacks on the intelligence community's surveillance powers.

Trump has largely hinged those grievances on the FBI's handling of surveillance against a former adviser to his campaign, Carter Page, in 2016 and 2017. A DOJ inspector general report found significant inaccuracies and omissions in the applications for court-authorized wiretaps against Page.

But that program is entirely separate from the FISA program that the administration is currently appealing to Congress to reauthorize before its end of year expiration, which doesn't involve court approved warrants.

For comparison, in 2021 officials identified more than 230,000 instances in which non-U.S. persons were targets of Section 702 warrantless surveillance. That same year officials only sought FISA court-authorized surveillance against more that 370 Americans or non-U.S. citizens inside the country, according to the most updated data from the DNI.

Olsen, though, acknowledged Tuesday the valid criticism of cases when officials have been found to have misused the Section 702 program. An audit late last year outlined several times when FBI officials used the 702 search query system using Americans' identifiers for unauthorized purposes.

In certain cases, such queries would be proper if an official was seeking to identify an American who could be considered a victim of foreign hacking or spying. But the audit found cases in which it said officials appeared to have misunderstood the rules and used the program to screen potential informants for any damaging information and one case where an agent queried the name of a local political party to see if it had connections to foreign intelligence.

"At the end of the day, these mistakes are not acceptable," Olsen said. "They aren’t acceptable to us, are not acceptable to the court or Congress, and not acceptable to the public. Nor should they be."

Olsen said following the audit the FBI implemented several reforms that resulted in a dramatic drop in the total number of U.S. person queries.

"Of course, there are going to be compliance incidents in a complex system, involving human beings, trying to work on tremendously difficult problems under time pressure," Olsen said. "But the reality is that every mistake undermines public trust and confidence in how we use these tools."

Olsen said moving forward would require candid discussions with congressional leaders on the importance of reauthorizing the program, but repeatedly sought to underscore what he said could be dire implications for U.S. national security if the program lapsed for even a few days.

"I think it is very dire," Olsen said. "I can tell you from my own career going back to my time at the FBI in the 2000s to today, I have seen the way in which 702 has become increasingly important -- increasingly the tool that enables us to collect information that we have no other way of getting."