Democrats are getting an early preview of what a bare-knuckle brawl a general-election matchup between President Donald Trump and one of the top three Democratic primary contenders would be.

He'll paint Joe Biden as "sleepy" and senile. He'll bash Bernie Sanders as "crazy," underscoring his proposal to eliminate private health insurance. And he'll mock "Pocahontas" Elizabeth Warren for her past claims to Native American ancestry.

New evidence came Tuesday, when Trump's campaign manager Brad Parscale posted a video calling into question the former vice president's mental acuity. It spliced clips of Democratic rivals doing the same, alongside footage of Biden's verbal faux pas and TV reporters discussing concerns within the party about the front-runner's ability to handle a long and tough election.

The early hints at Trump's playbook point to the likely ugliness of the 2020 general election, which both parties are hyping as the most important in generations. Trump's tactics reveal a president who's unlikely to allow his own age, verbal blunders and checkered past to stop him from leveling attacks on his would-be rival for those same attributes.

In a way, it's a replay of Trump's strategy in 2016 against Hillary Clinton and some of his tactics in the White House - accusing his opponents of what he has been credibly accused of.

"That's Trump in a nutshell. You call him stupid; he says you're stupid," said Jeremy Mayer, a government professor at George Mason University. "You call him a liar; he calls you a liar."

When Clinton called him Vladimir Putin's "puppet," Trump replied, "No puppet, you're the puppet." He raised alarms about Clinton's health despite being opaque about his own. He called her corrupt despite questions about his business empire. He bashed Sen. Al Franken of Minnesota over sexual harassment allegations despite facing accusations by more than 20 women of sexual misconduct.

Mayer called it a "jiujitsu" strategy that builds on a tactic used by Republican operative Karl Rove, who believed in turning an opponent's strength into a weakness. Instead, he said, Trump projects his own electoral weaknesses onto his opponents.

Speaking at the Republican retreat in Baltimore at the same time as the third Democratic debate, Trump depicted Biden as too exhausted to stand up to China.

"He's fallen asleep. He has no idea what he's doing or saying," the president said last Thursday, offering a mockery of a tired Biden during a potential negotiation with Chinese leader Xi Jinping. "What? Where am I? 'Just sign here, Sleepy Joe, just sign here.'"

Trump is 73. Biden is 76. The president faces regular criticism for delivering long and rambling answers to questions and for lacking coherence when discussing policy issues. Although Trump was said to be otherwise healthy, his physical exam released in 2019 found him to be obese under the standards of the National Institutes of Health.

When it comes to Warren, who's risen steadily over the summer to a virtual second-place tie with Sanders, Trump lamented last week that he started mocking her claims to Native American ancestry too soon.

"I hit Pocahontas way too early. I thought she was gone. She's emerged from the ashes. And now it looks like she could beat Sleepy Joe," he said last week in Baltimore.

Trump's attack evokes the most damaging blunder of Warren's presidential effort. After releasing a DNA test last October showing that she was between 1/64 and 1/1024 Native American, Warren faced fierce criticism for making a claim to American Indian ancestry on the basis of blood while lacking such experience growing up as a white woman. She apologized privately to the Cherokee Nation in February, and offered a public mea culpa at a forum for American Indian issues in August.

Still, Trump - who has been credibly accused of misrepresenting his own past, from exaggerating his wealth to making hush money payments to porn stars he allegedly had affairs with - suggested he'll revive the attack on Warren.

"The Pocahontas thing - I did that, it was before its time. Too early. One-thousand twenty-fourth. That means I have more Indian blood than she does and I have none," he said in New Mexico. "Get me another 4%. Maybe another 10%. But I was early with her and, frankly - oh, it's coming back, don't worry about it."

As for Sanders, the president has mocked him as "a socialist-slash-communist" since the 2016 campaign, when the Vermont senator finished as the runner-up for the Democratic nomination.

"Crazy Bernie, he is a crazy guy," Trump said in Baltimore, taking aim at his health care legislation that would replace private insurance with an expanded Medicare program that covers all Americans.

Trump said the Medicare for All plan would "dramatically raise middle class taxes" and "eliminate private insurance for 180 million Americans."

Trump lacks a health-care alternative to the status quo, and his party was hammered in the 2018 congressional elections for attempting to repeal the Affordable Care Act, or Obamacare. But that isn't stopping him from making a target of the Democrats' health care proposals.

"I've never seen anyone in politics who can turn an attack backwards as well as Trump," Mayer said.

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Bloomberg's Ryan Teague Beckwith contributed.