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 the discreditor in chief.

In his short political career, Trump has been all about sizing up opponents and then tearing them down, one by one.

Think “low-energy Jeb” Bush, “Lyin’ Ted” Cruz and “Crooked Hillary” Clinton.

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The insults, which serve to fire up Trump’s base and poison people against his political enemies, have served the president well, contributing to his extraordinary rise in 2016.

“He's very effective at making it personal,” said Susan Del Percio, a Republican strategist who has frequently opposed Trump’s positions.

“This is exactly how a billionaire TV personality became more relatable,” she said. “He breaks it down to a common denominator. And what's so appealing to his supporters is he does it so convincingly. He's not trying to hedge his bets. He's never backing down, and that's attractive to a certain group of voters. It keeps him real.”

Since taking office, the president hasn’t slowed down with his takedowns of political opponents, including “nut job” James Comey James Brien ComeyDemocrats fear Russia interference could spoil bid to retake Senate Book: FBI sex crimes investigator helped trigger October 2016 public probe of Clinton emails Trump jabs at FBI director over testimony on Russia, antifa MORE, the former FBI director whose firing directly led to the appointment of special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE.

But in Mueller, a war hero and legendary FBI man, Trump arguably faces his biggest challenge.

To date, Trump hasn’t really come up with a belittling nickname for Mueller. For nearly the entire first year of the probe, Trump’s attorneys advised him to cooperate with the special counsel, believing that was the best way to persevere.

The strategy has changed in recent months with the remade Trump legal team now led by the pugnacious former mayor of New York City, Rudy Giuliani, who like the president is a headline maker who enjoys duking it out in the press.

It’s led to a more heads-on strategy of dealing with the special counsel’s probe, even if it hasn’t yet produced the kinds of personal attacks Trump made famous in the presidential campaign.

Nonetheless, the Trump discrediting machine is at full force when it comes to the special counsel probe, or the “Russian Collusion Witch Hunt,” as Trump describes it on Twitter.

In another attack line, Trump uses the phrase “13 angry Democrats” to criticize the Mueller team and the Obama administration officials overseeing the FBI in 2016. The point is to label Trump as the victim of a deep state conspiracy led by his political opponents, sidestepping the argument that Mueller is a lifelong Republican and that his investigation is now overseen by Deputy Attorney General Rod Rosenstein Rod RosensteinDOJ kept investigators from completing probe of Trump ties to Russia: report Five takeaways from final Senate Intel Russia report FBI officials hid copies of Russia probe documents fearing Trump interference: book MORE, a Republican appointed to his position by Trump.

“When will the 13 Angry Democrats (& those who worked for President O), reveal their disqualifying Conflicts of Interest? It’s been a long time now! Will they be indelibly written into the Report along with the fact that the only Collusion is with the Dems, Justice, FBI & Russia?” Trump tweeted on Saturday.

The attacks on the special counsel probe appear to be having the desired effect.

A Monmouth University poll out earlier this month showed that the number of people who want to see the Mueller investigation carry on is decreasing. The poll showed that 54 percent of those surveyed want to see the probe continue, shrinking from 60 percent in March.

Shermichael Singleton, another Republican strategist who has disagreed with Trump on various issues, said the president’s argument on Mueller is resonating.

“He's doing a good job of saying, 'We don't know what they're doing. I think that's why his attacks are sticking so well because people are wondering, ‘Well, what are we really doing with this thing?’”

Old rivals echo Singleton.

“He is speaking directly in a way that no one has,” said Philippe Reines, a longtime top adviser to Clinton who helped the 2016 Democratic nominee prepare for the presidential debates by playing Trump. “He’s using [Twitter] in a really simple way. He's using it like he's emailing people individually. It's the next best thing to calling people on the phone.”

Most of Trump’s opponents fight back, though to little effect.

Mueller is different, however. The special counsel’s team says little publicly, leaving Trump’s attacks to be answered mostly by Democrats or officials from the Obama administration such as former CIA Director John Brennan John Owen BrennanJournalism or partisanship? The media's mistakes of 2016 continue in 2020 Comey on Clinton tweet: 'I regret only being involved in the 2016 election' Ex-CIA Director Brennan questioned for 8 hours in Durham review of Russia probe MORE or former Director of National Intelligence James Clapper James Robert ClapperOn China, Biden is no Nixon — and no Trump The Hill's 12:30 Report - Speculation over Biden's running mate announcement Trump slams former intelligence officials to explain 'reluctance to embrace' agencies MORE.

Del Percio worries the attacks will have a lasting impact on how the investigation is viewed.

“It's not Mueller's place to respond, and meanwhile you have the president harping on this every single day,” she said.

Those who have followed Trump’s career note that he made his name by going for the jugular as a real estate mogul.

Reines said the president’s style is effective because it’s genuine to Trump and his base.

“It’s effective in its simplicity. … There’s no hesitation,” he said. “He is talking to his audience and he understands the room.”

At the same time, in studying hours of Trump tapes to help Clinton prepare for the debates, Reines said the tactic also belies certain weaknesses in Trump — that an opponent has gotten under his skin, or that Trump wants to change the subject.

When opponents have tried to bully the bully in the schoolyard, it has backfired.

After Trump labeled 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.) “Little Marco,” the Florida senator needled Trump for his “spray tan” and his “small hands.”

But the insult-laden attacks fell flat.

“[Rubio] overdid it,” Reines recalled. “He went for the jugular and you can't shift like that. ... When Marco Rubio started to fight fire with fire it was disingenuous. It was just jarring.”

Mueller isn’t going to be firing back at Trump over Twitter or in interviews on cable television. But as he seeks to move forward with his probe, he and his team will need to have an eye on public opinion.