Washington DC - Former US president Joe Biden said Thursday he was not surprised Kamala Harris lost the 2024 election to Donald Trump and blamed her defeat on Republicans taking the "sexist route."

Biden, in an interview with ABC's The View, also denied claims made in recent books that he had suffered a cognitive decline in his final year in office.

"They are wrong. There's nothing to sustain that," the 82-year-old said.

Former First Lady Jill Biden, who appeared on the show too, also rejected the allegations of her husband's mental decline and denied claims that she had created a "cocoon" around him at the White House.

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"The people who wrote those books were not in the White House with us and they didn't see how hard Joe worked every single day," she said. "He wasn't hiding somewhere. I didn't have him, you know, sequestered in some place."

Biden said the sole reason he abandoned the presidential race was "because I didn't want to have a divided Democratic Party."

The former president also launched a few jabs at Trump, saying his Republican successor has "had the worst 100 days any president's ever had."

"I think he has done, quite frankly, a very poor job in the interests of the United States of America," he said.

Asked about Harris's loss to Trump, Biden said he was disappointed but "wasn't surprised – not because I didn't think the vice president was qualified first to be president – she is."

"I wasn't surprised because they went the sexist route... this is a woman, she's this, she's that," he said.

"I've never seen a quite as successful and a consistent campaign undercutting the notion that a woman couldn't lead the country, and a woman of mixed race," Biden said.

The former president also said he talks to Harris frequently and "she's got a difficult decision to make about what she's going to do."

"I hope she stays fully engaged," he said.