President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE is doing what he does best: Giving potential enemies bad brands.

Joe Biden Joe BidenOmar fires back at Trump over rally remarks: 'This is my country' Trump mocks Biden appearance, mask use ahead of first debate Trump attacks Omar for criticizing US: 'How did you do where you came from?' MORE is “one percent Biden,” a nickname that mocks the vice president’s poor showings in two previous runs for the White House.

Sen. Corey Booker (D-N.J.) is the “bad mayor” who “destroyed, practically by himself” the city of Newark, N.J.

Most controversially, Sen. Elizabeth Warren Elizabeth WarrenHarris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda Judd Gregg: The Kamala threat — the Californiaization of America GOP set to release controversial Biden report MORE (D-Mass.) is “Pocohontas,” the nickname Trump first placed on Warren because of her identification as a Native American in academic listings.

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Republicans have sometimes been unsettled by Trump's name calling, but as 2020 inches closer and the Democratic field comes into view, many say the president is doing what he does best; getting a head start on the labels that could doom his future opponents.

“This could very well be the start of his branding campaign against possible 2020 candidates,” said Ron Bonjean, the longtime Republican political operative who has advised the White House. “He successfully branded many of his competitors and I think he knows that defining these people early and often could be beneficial down the road.”

Trump has experience to suggest the strategy can be successful.

During the 2016 Republican primary, he tagged Florida Gov. Jeb Bush with the “low energy” moniker, something Bush never fully recovered from.

Sen. Marco Rubio Marco Antonio RubioOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Democrats step up hardball tactics as Supreme Court fight heats up Press: Notorious RBG vs Notorious GOP MORE (R-Fla.) was named “Little Marco,” while Trump’s Democratic opponent was “Crooked Hillary” Clinton, a name he and his supporters have continued to use nearly two years later.

“It was effective against Republican primary opponents and it will likely be effective this time around,” Bonjean said.

Barry Bennett, who served as a senior adviser to the Trump campaign, added that Trump is going to continue to highlight the hypocrisy and weakness in the Democratic Party by calling out specific would-be opponents.

“They are shiny examples of the problems inside the Democratic Party,” Bennett said. “They are behaving like huge hypocrites…and they look like fools. It’s helping to energize our base. They’re doing us a favor.”

Trump has fired back at Democrats as they have turned up the heat on him.

Booker has been increasingly critical of Brett Kavanaugh, Trump’s nominee to the Supreme Court. Earlier this week, he urged the president to walk away from Kavanaugh and select a different nominee saying it’s about his temperament.

At a town hall in Massachusetts over the weekend, Warren slammed Trump “for taking the country in the wrong direction.”

“Working people have taken one punch to the gut after another,” she said. “And I am worried down to my bones about what Donald Trump is doing to our Democracy.”

Biden called Trump’s response to the late Sen. John McCain John Sidney McCainCindy McCain endorses Biden: He's only candidate 'who stands up for our values' Biden says Cindy McCain will endorse him Biden's six best bets in 2016 Trump states MORE’s death “almost un-American.” He also ripped Trump’s “naked nationalism.”

“The worst thing in the world we can have is this new naked nationalism, America first,” Biden said at the University of Pennsylvania last month, according to CNN. “The worst thing in the world we can have is this new naked nationalism, America first. I believe making America first in the way we’re doing it will make America last.

On Wednesday, Sen. Kamala Harris Kamala HarrisButtigieg stands in as Pence for Harris's debate practice First presidential debate to cover coronavirus, Supreme Court Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (D-Calif.) another potential 2020 candidate, urged Trump to “stop being mean” after he mocked the testimony of Christine Blasey Ford, who has accused Kavanaugh of sexually assaulting her.

“I’m embarrassed that the President of the United States would do that to this woman,” Harris said.

It was a sentiment that will likely provoke Trump to unleash during his next rally, political observers say.

“If you’re at all critical of him, you’re an opponent and need to be responded to,” said Cal Jillson, a professor of political science at Southern Methodist University. “He is who he is and no criticism goes unanswered…And if you can define your opponent and demean them, that’s a good day’s work to him.”

Most of all, he revels in the fight, Jillson said.

“I think the part of it that he enjoys the most is the sword fighting and the roar of the crowd and energy that comes with it. It’s so important to him. And I expect he’ll be very much the same guy in 2020.

Bennett acknowledged that sentiment, saying Trump is not only good at defining his opponents. He’s also relentless, he said.

“You can fight him if you want but he won't stop fighting back,” he said. “I think he learned early on that you can't lose a fight unless you stop fighting back.”