President Donald Trump in the Cabinet Room of the White...

President Donald Trump in the Cabinet Room of the White House on June 13. Credit: AFP / Getty Images / Mandel Ngan

President Donald Trump for years has wielded derogatory nicknames to great effect against his political opponents.

The Democratic candidates seeking to unseat him in 2020 are only the latest of his targets.

But “SleepyCreepy Joe” Biden, “Crazy Bernie” Sanders, Elizabeth “Pocahontas” Warren and others now confront a crucial challenge: how to respond to a rival who goes low and gets personal.

The party, after all, has lessons to learn from Hillary Clinton’s defeat in 2016, said Steve Schale, a Florida-based Democratic strategist.

Trump repeatedly called Clinton “crooked,” hammering the insult into Americans’ psyches.

“A lot of Democrats — me included — made the mistake of discounting Trump’s nonstop attacks on Secretary Clinton,” said Schale, an alumnus of Barack Obama’s 2008 and 2012 campaigns. “It’s easy to lull yourself into thinking this stuff doesn’t matter, but at some level, it did.”

Biden, thus far this election cycle, has been in Trump’s crosshairs the most of the Democratic presidential contenders.

Trump has questioned the former vice president’s mental and physical fitness, as he did with Clinton.

“I like running against people who are weak mentally. I think he is the weakest up here,” Trump said earlier this month, pointing to his head.

Biden, whose reponses to Trump have ranged in tone, that same day called the president a “threat to our core values.”

Some of the tweets from Biden’s campaign account have been more sardonic. “President Trump thinks his tariffs are being paid by China. Just like he thinks Mexico is building the wall,” one read earlier this month.

Then, there were Biden's remarks last year that he would have “beat the hell out of” Trump if they were in high school, citing the president’s lewd comments about women.

Sanders, the independent senator from Vermont, whose mental acuity also has been under attack by Trump, similarly has confronted Trump head-on.

He has labeled the president a racist and a xenophobe.

Sanders last week condemned the “lies, distortions and total, absolute nonsense” in Trump’s re-election campaign kickoff speech in Orlando.

“You don’t have to respond in kind, but you have to respond with force,” said Basil Smikle, a political consultant and former executive director of the New York State Democratic Party. “It’s important to engage him and not seem like you’re not shrinking away.”

Sen. Warren (D-Mass.) and Mayor Pete Buttigieg of South Bend, Indiana, “have been really good at pivoting to a broad context and themes that are resonating with voters and not necessarily turning away tons of people who don’t like the back-and-forth,” Smikle said.

Trump has tagged Warren “Pocahontas,” a racially charged reference to her claim that she has Native American ancestry. He has taken digs at Buttigieg’s appearance, calling him “Alfred E. Neuman,” the face of Mad Magazine.

When the president mocked her for getting a DNA test to prove her ancestry, Warren in January responded that Trump “can bluster forever, but it doesn’t change the underlying reality.” She ticked off stagnant wages and rising health care costs as among the problems under Trump.

Buttigieg, asked during a Fox News town hall last month about Trump’s character attacks, earned loud audience applause when he responded: “The tweets are — I don’t care.”

But there are more traditional mudslingers in the crowded field of Democratic hopefuls, too.

New York City Mayor Bill de Blasio has stood out in that he borrowed from Trump’s playbook and assigned the president a disparaging nickname: “Con Don.”

“If you’re going to take on Donald Trump, it sure helps to be able to fight back and understand how to deal with him,” he told MSNBC last month.

A former de Blasio adviser and veteran strategist said he wishes the mayor wouldn’t go there.

“Civility is really what I would recommend to him,” said George Arzt, who worked on de Blasio’s successful city public advocate bid and was press secretary to the late Mayor Ed Koch. “Con Don, really? It’s just what the president is doing and one of the defining features of the president’s campaign.”

Washington, D.C.-based Democratic consultant Brad Bannon said the prevailing strategy for the party's contenders should to be to focus on health care and Trump’s broken promises, all the while acting as little like the president as possible.

“Democrats have to avoid getting down in the dirt with Trump,” Bannon said. “That’s one of Trump’s problems, he’s so mean-spirited.”

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Arrest in wrong-way DWI on LIE … St. Jude relic on LI … Mike DelGuidice album release party Credit: Newsday

LI man arrested for arson ... Arrest in wrong-way DWI on LIE ... Wind farm sends power to LI ... Mike DelGuidice album

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