One of Biden's dogs has been involved in 'biting incidents.' Here's a timeline of Champ and Major's life at the White House.

In a December interview with CNN's Jake Tapper, Biden revealed that he fractured his foot after tripping on a rug that Major displaced while chasing a ball.

"I got a dog. And anybody who's been around my house knows, dropped — the little pup dropped the ball in front of me, and for me to grab the ball," he said.

He continued: "And I'm walking through this little alleyway to get to the bedroom, and I grabbed the ball like this and he ran. And I'm joking, running after him and grab his tail. And what happened was that he slid on a throw rug, and I tripped on the rug he slid on."

Biden wore a boot for several weeks in December as the fracture healed.

The Bidens adopted Major from the Delaware Humane Association in 2018.

The Zoom "indoguration" event featured NBC "Today" show contributor Jill Martin and other rescue dogs with their owners to raise money for the shelter.

"We are elated," Cory Topel, the shelter's marketing manager, told Insider in an email at the time. "With Major heading to the White House, we hope it will shine light on the importance of animal adoption, as well as supporting your own local animal shelter."

The dogs joined the first couple at their new residence days after the inauguration, Michael LaRosa, Jill Biden's press secretary, confirmed to Insider in January.

"The first family wanted to get settled before bringing the dogs down to Washington from Delaware," LaRosa told Insider. "Champ is enjoying his new dog bed by the fireplace and Major loved running around on the South Lawn."

Champ and Major made their White House television debut to remind people to mask up.

Dr. Jill Biden filmed a coronavirus public service announcement with the German shepherds that aired during Animal Planet's Puppy Bowl XVII on Super Bowl Sunday.

"For a lot of us during this pandemic, our pets have been such a source of joy and comfort — and maybe a bark or two on a video conference," she said, sitting in front of a fireplace at the White House with Champ and Major at her feet. "The unconditional love from a dog is one of the most beautiful things on Earth, and we owe it to them to keep ourselves healthy."

Biden then reminded people to keep wearing masks, even when out walking their dogs.

"They have to take the elevator. They're not used to that," she told Clarkson. "They have to go out on the South Lawn with lots of people watching them. So, you know, that's what I've been obsessed with, just getting everybody settled and calm."

Major and Champ returned to the Bidens' estate in Wilmington, Delaware, after Major displayed aggressive behavior and bit a member of the Secret Service, CNN reported.

The CNN report indicated that Major had previously been known to display agitated behavior, which included "charging" at staff and security officers, jumping, and barking. Sources told CNN that Champ, in comparison, was "slowed down" due to his old age.

White House press secretary Jen Psaki said at a press conference in March that Champ and Major were "still getting acclimated and accustomed to their surroundings and new people," and that Major "was surprised by an unfamiliar person and reacted in a way that resulted in a minor injury to the individual."

The dogs were previously scheduled to return to Delaware while Jill Biden traveled, but they were sent home after the "biting incident," where Major received special training.

"Major was a rescue pup," Biden told ABC News' George Stephanopoulos. "Major did not bite someone and penetrate the skin. The dog's being trained now with our trainer at home in Delaware."

Biden said that living in a new, different environment at the White House has been difficult for his dog.

"You turn a corner, and there's two people you don't know at all," Biden said. "And he moves to protect. But he's a sweet dog. 85% of the people there love him ... All he does is lick them and wag his tail."

Psaki told reporters at a March 24 briefing that Champ and Major joined the first family at Camp David in Maryland over the weekend before returning to the White House on March 21.

"The dogs will come and go, and it will not be uncommon for them to head back to Delaware on occasion, as the president and first lady often do as well," Psaki said.

On Monday afternoon, Major bit a National Park Service employee while out on a walk, LaRosa confirmed to CNN.

"Yes, Major nipped someone on a walk," the first lady's spokesman told the outlet. "Out of an abundance of caution, the individual was seen by WHMU [the White House Medical Unit] and then returned to work."

It has not yet been announced whether Major will remain in the White House or receive additional training.