(CNN) President Donald Trump appears prepared to wage wholesale political war with the last person who held his office, convinced his predecessor committed a crime worthy of investigation -- despite being unable to name the crime or provide any evidence for it.
Even the acknowledgment by Trump's attorney general that criminal charges weren't expected against former President Barack Obama and former Vice President Joe Biden appeared unlikely to quiet Trump's unrelenting assault.
"I have no doubt that they were involved in this hoax, one of the worst things ever to befall this country in terms of political scandal," Trump said at the White House on Monday without offering any more clarity or proof of his claims.
Escaping the White House for another weekend at Camp David, Trump appeared "highly focused" on Obama over the course of Saturday and Sunday, a person familiar with the matter said.
As he huddled in the mountainside retreat's rustic cabins with a roster of Republican lawmakers -- many of whom forged national profiles defending Trump during his impeachment proceedings -- Trump discussed ways to advance the baseless conspiracy about the former president, the person said.
When Trump returned to the White House on Sunday, he deemed Obama an "incompetent president" after his predecessor took veiled swipes at his handling of the coronavirus pandemic during Saturday commencement addresses.
"That's all I can say," Trump said before walking into the White House. "Grossly incompetent."
Between Friday and Monday, Trump tweeted or retweeted about Obama 19 times and seemed prepared to continue his assault. His lines of attack fell into two categories: the former president's preparation for global pandemics -- which Trump has claimed was woefully inadequate -- and the as-yet-unspecified criminality, which appears to center on claims of sinister attempts to derail Trump's campaign and presidency.
The unprecedented animus between the sitting and former presidents -- who have met in person only once since parting ways on Inauguration Day in 2017 -- is poised to become a running thru-line of the next five-and-a-half months as Trump seeks to move on from a deadly pandemic and battles Biden for re-election.
Attorney General William Barr's declaration Monday that neither Obama nor Biden is likely to be charged by his department as part of an investigation into the origin of the Russia probe only highlighted how much Trump will likely lean on his allies in Congress to advance his conspiracy.
"As long as I'm attorney general, the criminal justice system will not be used for partisan political ends," Barr said at a news conference, adding: "Not every abuse of power is a federal crime."
Later in the day, Trump said he was "surprised" by Barr's comments.
"I think if it was me they would do it," the President said during a meeting of restaurant executives who had been summoned to the White House to discuss their cratering industry.
Obama, who has steadfastly avoided getting into drawn-out arguments with his successor, waded in more directly to the fray on Saturday evening when he delivered a pair of televised commencement addresses that were broadcast nationally.
The mere fact Obama was invited to participate in the event -- designed to give graduating seniors a commencement experience when their in-person events were canceled -- was bound to irritate Trump, who was not involved. Trump will deliver a commencement address next month at the US Military Academy West Point, but unlike Obama, he wasn't urged in online petitions for a major national address.
In his remarks, Obama did not name Trump. But his assessment of how the coronavirus has been handled in the United States was scathing nonetheless and carried clear rebukes of the current President.
"All those adults that you used to think were in charge and knew what they were doing? It turns out that they don't have all the answers," Obama said during a prime-time special for high school seniors, which was aired on major broadcast and cable television networks. "A lot of them aren't even asking the right questions. So, if the world's going to get better, it's going to be up to you."
In remarks earlier in the day to graduates of historically black colleges and universities, Obama again did not name Trump. But his rebuke of how the current President has handled the worst public health crisis in a generation was plain.
"More than anything, this pandemic has fully, finally, tore back the curtain on the idea that so many of folks in charge know what there doing. And some of them are not even pretending to be in charge," Obama said. While delivering a piece of advice in the second set of remarks, he attacked "so-called grown-ups" for "why things are so screwed up."
Though the subject of Obama's criticism went unspoken, it was obvious to many listeners that he was talking about Trump. White House press secretary Kayleigh McEnany responded by insisting Trump's "unprecedented coronavirus response has saved lives" and that he was left to "fill the stockpile left depleted by his predecessor" -- a claim CNN has repeatedly fact checked.
Over the past week, Trump has repeatedly invoked Obama as he looks to defend his own handling of the coronavirus pandemic. Trump spent weeks downplaying the severity of the virus, the federal government's response was hampered by delays in testing and gaps in supply chains for equipment and supplies, and last week, the head of the US Centers for Disease Control and Prevention said the US death toll would pass 100,000 by the start of June.
The uneven federal response, paired with skyrocketing unemployment, has led to concerns about Trump's political standing among Republican operatives and officials. Trump has sought to turn the page by encouraging states to lift stay-at-home orders, hoping for an economic rebound by November's election.
But he has also sought to divert blame for the crisis on the previous administration, turning the crisis into a referendum on how prepared Obama and Biden were for such a pandemic -- despite Trump having been in office for more than three years when the virus struck.
Using misleading claims, he's also repeatedly harkened to the previous administration's handling of the H1N1 swine flu -- despite a drastically higher death toll from coronavirus.
Obama administration officials have rejected the claims and pointed to the various pandemic preparation plans they left the incoming administration in 2017. And Obama himself has taken to tweeting articles and studies about the pandemic that encourage staid scientific judgment over politically tinged decision-making.
Trump, meanwhile, has added additional conspiracies into the mix as he looks to undermine Obama and Biden's administration. For years, Trump has claimed without proof that Democratic partisans within the Justice Department and the FBI abused their powers to investigate members of his campaign and undermine his presidency. His latest claims against Obama appear to be an extension of the same underlying theory, which is part of the President's sustained effort to rewrite the history of the Russia investigation.
There is no evidence that Obama directed any action by the FBI against Trump's campaign before the 2016 election, but Trump has fanned the flames of that conspiracy since at least 2017, when he tweeted that Obama "had my wires tapped," an accusations that people familiar with the matter said enraged the former president.
Trump raised the unfounded claims at various intervals over the past three years, but has amplified them anew as the pandemic continues to rage and his political standing seems threatened.
Trump has encouraged friendly lawmakers to take steps to advance the claims, including by demanding Obama appear before their committees.
"If I were a Senator or Congressman, the first person I would call to testify about the biggest political crime and scandal in the history of the USA, by FAR, is former President Obama," Trump wrote on Twitter last week. "He knew EVERYTHING."
At Camp David this weekend, Trump was joined by several lawmakers who gained prominence by their aggressive support of him during House impeachment hearings — including Republican Reps. Jim Jordan of Ohio, Elise Stefanik and Lee Zeldin of New York, Devin Nunes of California, and Matt Gaetz of Florida, along with his new chief of staff Mark Meadows and his wife Debbie.
As he returned to the White House, Trump did not say how he might work to advance his Obama claims.
"I think a lot of things have happened, very good, very -- it was a working weekend," Trump said. "It was a good weekend. A lot of very good things have happened."