Department of Energy officials are unable to get in touch with some critical nuclear workers with the National Nuclear Security Administration (NNSA) as they frantically attempt to rehire them, according to an internal email obtained by ABC News.

"The termination letters for some NNSA probationary employees are being rescinded, but we do not have a good way to get in touch with those personnel," the email reads.

The email asks managers to contact their employees directly because many of the terminated employees lost access to email and other government systems. Most managers are resorting to calling and texting their fired staffer’s personal phone numbers, ABC News has learned.

On Thursday, in a wave of firings across the federal government, the administration terminated roughly 300 employees with the NNSA, which is responsible for maintaining the U.S. nuclear stockpile, among other key nuclear functions.

ABC News was first to report that, after realizing the critical role these employees play in national security, the Department of Energy paused most terminations Friday and sought to "rehire" some employees.

The rehiring is currently underway. It’s unclear how many will ultimately return to work.

-ABC News' Jay Obrien

Upon returning to Palm Beach following his lap around the Daytona 500 speedway, President Donald Trump chatted with reporters as he disembarked Air Force One, primarily fielding questions about the Russia-Ukraine war.

“We're moving along. We're trying to get peace with Russia, Ukraine, and we're working very hard on it. It's a war that should have never started,” Trump said.

When asked what he believes Russian President Vladimir Putin's intentions are regarding Ukraine, Trump said he believes the leader ultimately wants the war to end.

"I think he wants to stop fighting -- I see that," Trump said while noting how Steve Witkoff, special envoy to the Middle East, met with Putin Sunday.

"We spoke long and hard. Steve Witkoff was with him for a very extended period -- like about three hours. I think he wants to stop fighting,” Trump said.

-ABC News' Kelsey Walsh

About 700 people have had their roles terminated at the Centers for Disease Control and Prevention (CDC), multiple sources told ABC News.

Before the sweeping terminations, approximately 13,000 personnel were employed at the agency. The 700 people do not include people that accepted deferred resignations, sources said.

None of the agency's top disease investigators are among those losing their jobs, but more than 100 recent graduates who served in fellowships at the agency had their roles eliminated, sources said.

-ABC News' Eric Strauss, Youri Benadjaoud, Mark Abdelmalek and Anne K. Flaherty

Trump on Sunday attended the Daytona 500 in Daytona Beach, Florida -- his second trip to the race as sitting president.

Trump did a fly-by of the track aboard Air Force One before taking a couple laps around the track in The Beast, the president’s armored limousine.

The president was awarded a jacket at the track, which he donned before meeting with NASCAR officials, drivers and some special guests before the race started.

The race was in a rain delay as Trump boarded Air Force One for his return to Palm Beach, Florida.