Former President Joe Biden has made several appearances in recent weeks that have raised his profile in a way unusual for a recent ex-president, providing a platform for him to criticize President Donald Trump as dishonest, bullying and "vacant."

The appearances have also allowed Biden to defend his own legacy at a time when Trump frequently blames him by name, many Democrats remain frustrated that he took so long to end his 2024 presidential campaign and a pair of recent books assert that Biden's team hid his cognitive decline at the end of his presidency.

"They are wrong," Biden said of the assertions about his decline in an appearance Thursday on ABC's "The View." "There is nothing to sustain that."

The result is a striking dynamic in which two presidents — each the other's successor as well as his predecessor — are engaged in a public back-and-forth over whether one wrecked the economy or the other is embarrassing America. While Trump blames Biden for the economy and the border, Biden is defending his legacy in the face of attacks on Social Security and free trade.

One Democrat thinks he knows why Trump can't stop talking about his predecessor.

"Trump is suffering a significant erosion in his job approval. He has to have somebody to blame, and he is deflecting as much attention as he can on Joe Biden," said former U.S. Rep. Steve Israel (D-New York). "Silence by Joe Biden would be a win for Trump; it validates Trump's absurd charges. So being quiet is not an option."

Still, some Democrats worry that Biden's reemergence plays into Trump's hands. In Thursday's appearance on "The View," Biden was asked why he thinks Trump mentions him so often, sometimes multiple times a day. Biden suggested it is because he is the only politician to have defeated Trump electorally.

"I beat him," Biden said emphatically. "I'm used to dealing with bullies." But he also accepted responsibility for Trump's victory last year, saying, "I was in charge and he won, so I take responsibility."

If Biden occupies a special place in Trump's psyche, the reverse is also true. Biden ran for president in 2020 to drive Trump out of the White House, winning a dramatic victory only to see that legacy eclipsed by Trump's comeback last year.

Biden and Trump's fates have been bitterly entwined since Trump entered politics in 2016. Biden, then the outgoing vice president, chose not to seek the White House, ceding the field to Hillary Clinton, who proceeded to lose to Trump in an upset.

Trump, of course, still wrongly denies that he lost to Biden in 2020. And after Biden stepped aside in 2024, he watched his nemesis defeat his chosen successor, Vice President Kamala Harris.

Now Trump and Biden have likely run their final races. Yet their political battle still shows no sign of ending.

Biden broke his silence less than three months after Trump's Jan. 20 inauguration with a blistering attack on the U.S. DOGE service's efforts to overhaul the Social Security program. "In fewer than 100 days, this administration has done so much damage and so much destruction," Biden told a gathering of representatives of the disabled. "It's breathtaking that it could happen so fast."

He was sharper in an interview with BBC News on Monday, taking aim at Trump's suggestions that the United States should take over Greenland, Canada and the Panama Canal. "What the hell's going on here? What president ever talks like that?" Biden said. "That's not who we are. We're about freedom, democracy, opportunity — not about confiscation."

On "The View," Biden essentially called Trump a failure and a liar. "He's had the worst 100 days any president has ever had," Biden said. "I would not say honesty has been his strong point."

The White House responded by deriding Biden's mental capacity.

"Joe Biden is a complete disgrace to this country and the office he occupied," said Steven Cheung, the White House communications director. "He has clearly lost all mental faculties and his handlers thought it'd be a good idea for him to do an interview and incoherently mumble his way through every answer. Sadly, this feels like abuse."

Trump and his team are not alone in taking aim at the 82-year-old ex-president. Two recent books contend that Biden and his aides were deceptive, deluded or both about his declining capacity last year, making a reckless decision to run for reelection that ended only after a faltering debate performance in June.

"Original Sin," by Jake Tapper and Alex Thompson, is subtitled, "President Biden's Decline, Its Cover-Up, and His Disastrous Choice to Run Again." Another book, "Uncharted: How Trump Beat Biden, Harris, and the Odds in the Wildest Campaign in History" by Chris Whipple, asserts that Biden's circle was engulfed in a "fog of delusion and denial."

Biden and his wife, former First Lady Jill Biden, strongly rejected that assertion in Thursday's appearance. "The people who wrote those books were not in the White House with us," Jill Biden said. "They did not see how hard Joe worked every single day. … I think he was a great president. If you look at things today, give me Joe Biden anytime."

Jill Biden also dismissed the notion that she had shielded her husband. "I did not create a cocoon around him," she said. "You saw him in the Oval Office. You saw him making speeches. I wasn't hiding him somewhere."

Some Democrats say privately they are not thrilled at Biden's reemergence, especially as Trump seeks to blame his predecessor for the country's problems. This echoes a moment in Trump's first term when some Democrats were unhappy that Clinton had begun speaking publicly; like Biden, she was grappling with what her party saw as an almost inexplicable loss.

Others are upset with Biden's suggestion that he could have beaten Trump if he had stayed in the race, saying that is tantamount to blaming Harris for the defeat.

"Kamala Harris was put in an impossible position with 100 days to go," Leah Greenberg, co-executive director of the liberal group Indivisible, posted on X. "She did her best to run a strong campaign without repudiating Biden. Biden has repaid her with shameful levels of disrespect and delusions about how he would have won. It's honestly sad and embarrassing."

Biden said Thursday he was not surprised Harris lost. But he made it clear he blamed Trump's tactics, not Harris's abilities.

"They went the sexist route: 'She's a woman, she's this, she's that,'" Biden said on "The View." "I've really never seen quite as successful and consistent a campaign undercutting the notion that a woman [could] lead the country, and a woman of mixed race."

Israel said Biden cannot let Trump refight the last election by ignoring his attacks in advance of the 2026 midterms, which could be critical to establishing guardrails for Trump's behavior.

"Trump is and will continue to do everything possible to put Joe Biden on the 2026 ballot, in an attempt to deflect attention from his own [low] approvals," Israel said. "President Biden has no choice."

Few would disagree that Trump's attacks on Biden have been relentless. When the president convened a Cabinet meeting on April 30 — as reports showed the U.S. economy had contracted — Trump began, "You probably saw some numbers today, and I have to start off by saying, that's Biden, that's not Trump."

Trump also made Biden's purported failures a central theme of his recent appearance on NBC's "Meet the Press." "I think he did a lot of very bad things, and despite some of the bad things, we're overcoming them," Trump said. "But he was bad on the border. He was bad on the economy. We had the worst inflation in the history of our country."

Leonard Steinhorn, who teaches communication and history at American University, said it is not surprising that Trump and Biden would still be locked in combat despite the tradition that presidents treat each other with deference.

"There is a lot of bad blood between these two," Steinhorn said. "From Trump's perspective, the worst thing you could be called is a loser, and he lost to Biden in 2020 … so it is lodged in his soul, his consciousness and his thinking that he has to do everything he can to diminish Joe Biden."

Steinhorn said that Biden, for his part, probably sees an opportunity to rewrite a narrative that his presidency was shadowed by inflation and questions about his mental capacity. Biden has stressed in his recent appearances that he enacted a sweeping national agenda in defiance of many analysts' predictions.

"I think he and his advisers see an opening right now, because people are scared economically," Steinhorn said. "The tariffs have been a gut punch, a solar plexus punch, to the American people. So if he can drive home the message that he handed off a good economy and Donald Trump is cratering it, that might move him up a peg or two."

Harris has also begun speaking out against Trump, marking his first 100 days in office on April 30 by condemning his "reckless" tariffs, his "unconstitutional demands" and what she called his efforts to silence dissent.

In the BBC interview, Biden dismissed the suggestion that his late withdrawal from the 2024 race had hurt the Democrats politically, saying he had turned over the campaign to a strong, well-funded candidate in Harris. But he acknowledged that walking away from reelection was not easy.

"I think it was the right decision," Biden said. "I think that … well, it was just a difficult decision."