Kristi Noem is speculated to be among the leading contenders to be Donald Trump's choice of a running mate.

In her new book, "No Going Back: The Truth on What's Wrong with Politics and How We Move America Forward," obtained by ABC News, South Dakota's Republican governor writes about killing her 14-month-old dog, Cricket, a wirehair pointer.

Noem describes the dog as having an "aggressive personality" and "was out of her mind with excitement."

According to the book, and first reported in The Guardian, things apparently came to a head for Noem, when, on the way home from a pheasant hunt, Cricket attacked a family's group of chickens, acting, she says, like a "trained assassin."

When Noem said she eventually got control of the dog, by grabbing her collar, she says, "she whipped around to bite me."

"I hated that dog," Noem reveals, claiming Cricket was "untrainable."

"This was my dog and my responsibility, and I would not ask someone else to clean up my mess," Noem writes. "I stopped the truck in the middle of the yard, got my gun, grabbed Cricket's leash and led her out into the pasture and down into the gravel pit."

"It was not a pleasant job," she writes, "but it had to be done."

Noem's stories of putting animals down don't end there.

After shooting her dog, Noem says she also killed a goat her family owned that she calls "nasty and mean." She described the goat as being a "problem for years," writing that male goats "urinate on their own heads and beards while in rut" and that the specific goat loved to chase her kids, scaring them.

Noem compares both decisions to put down the animals to a leader needing to make difficult decisions.

"It's often messy, ugly, and matter-of-fact, dealing with a problem that no one wants to deal with," she writes, adding, "I guess if I were a better politician I wouldn't tell the story here."

On Friday, Noem doubled down on X amid backlash over killing her dog.

"We love animals, but tough decisions like this happen all the time on a farm," Noem wrote. "Sadly, we just had to put down 3 horses a few weeks ago that had been in our family for 25 years."