As the Democratic presidential primary heats up, President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE has renewed his go-to campaign tactic of labeling his opponents with derogatory nicknames and targeting challengers with personal attacks.

Trump effectively dispatched a crowded field of Republican primary contenders in 2016, leaning on nicknames and insults like “Low Energy Jeb [Bush]” and “Lyin’ Ted [Cruz]” to belittle his opponents.

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With 24 Democratic candidates now in the race, the president has already targeted members of the primary field, slapping nicknames on several high-profile candidates as he tries to weaken his eventual general election competitor.

Here’s what Trump has said about some of the Democrats running for president.

Former Vice President Joe Biden Joe BidenBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Harris faces pivotal moment with Supreme Court battle MORE

Biden, who Trump reportedly views as one of his biggest challengers among the current Democratic candidates, has repeatedly drawn Trump’s ire both at rallies and over social media, garnering the nickname “SleepyCreepy Joe.”

“Looks to me like it’s going to be SleepyCreepy Joe over Crazy Bernie. Everyone else is fading fast!” Trump tweeted, referring to Biden and Sen. Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I-Vt.).

Looks to me like it’s going to be SleepyCreepy Joe over Crazy Bernie. Everyone else is fading fast! — Donald J. Trump (@realDonaldTrump) May 10, 2019

Trump had long referred to Biden as “Sleepy Joe” but added “Creepy” after several women alleged that the former vice president inappropriately touched them and made them feel uncomfortable.

The president last month made an offhand remark about rhyming the nickname.

“I thought to refer to him as Sleepy Joe, because a lot of people wanted me to take the word ‘sleepy’ to something that rhymes with it. Does that make sense to you? And I thought it was too nasty,” he told Fox News host Sean Hannity Sean Patrick HannitySunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Cruz: Trump should nominate a Supreme Court justice next week Ex-Pence aide: Trump spent 45 minutes of task force meeting 'going off on Tucker Carlson' instead of talking coronavirus MORE.

Trump and Biden have long feuded since the former vice president said last year that he would have "beat the hell out" of the president if they had gone to high school together, following comments the president made about women.

Sen. Bernie Sanders (I-Vt.)

Trump has dubbed Sanders “Crazy Bernie,” and often cites the self-proclaimed Democratic Socialist’s policies in his criticism of the Vermont senator.

Crazy Bernie has just entered the race. I wish him well! — Donald J. Trump (@realDonaldTrump) February 20, 2019

“Bernie’s crazy. But Bernie’s got a lot more energy than Biden, so you never know,” Trump said at an event this month. “Bernie’s got a lot of energy but it’s energy to get rid of your jobs.”

Sanders continues to rank near the top of national and statewide primary polls, but has recently found himself behind Biden since the former vice president launched his campaign last month.

Sen. Elizabeth Warren Elizabeth WarrenDimon: Wealth tax 'almost impossible to do' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context Democrats shoot down talk of expanding Supreme Court MORE (D-Mass.)

Warren has emerged as one of Trump’s most popular targets of ridicule, receiving the derogatory nickname “Pocahontas” over her controversial past claims of Native American ancestry.

“Today Elizabeth Warren, sometimes referred to by me as Pocahontas, joined the race for President. Will she run as our first Native American presidential candidate, or has she decided that after 32 years, this is not playing so well anymore? See you on the campaign TRAIL, Liz!” Trump tweeted shortly after Warren officially launched her presidential bid.

Today Elizabeth Warren, sometimes referred to by me as Pocahontas, joined the race for President. Will she run as our first Native American presidential candidate, or has she decided that after 32 years, this is not playing so well anymore? See you on the campaign TRAIL, Liz! — Donald J. Trump (@realDonaldTrump) February 9, 2019

Indigenous groups have slammed Trump over the nickname, saying it amounts to a slur.

“The name becomes a derogatory racial reference when used as an insult. American Indian names, whether they be historic or contemporary, are not meant to be used as insults. To do so is to reduce them to racial slurs,” the Alliance of Colonial Era Tribes said in a statement last year.

Warren has emerged as a vocal detractor of Trump’s policies, sometimes pivoting from his insults to criticize the White House.

“Hey, @realDonaldTrump: While you obsess over my genes, your Admin is conducting DNA tests on little kids because you ripped them from their mamas & you are too incompetent to reunite them in time to meet a court order. Maybe you should focus on fixing the lives you're destroying,” she tweeted last year, referring to Trump’s “zero tolerance” immigration policy that led to family separations at the border.

Hey, @realDonaldTrump: While you obsess over my genes, your Admin is conducting DNA tests on little kids because you ripped them from their mamas & you are too incompetent to reunite them in time to meet a court order. Maybe you should focus on fixing the lives you're destroying. — Elizabeth Warren (@ewarren) July 5, 2018

South Bend, Ind. Mayor Pete Buttigieg Pete ButtigiegThe Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice Hillicon Valley: FBI, DHS warn that foreign hackers will likely spread disinformation around election results | Social media platforms put muscle into National Voter Registration Day | Trump to meet with Republican state officials on tech liability shield MORE

Trump just recently started mocking the South Bend, Ind. mayor, focusing on his difficult-to-pronounce name and lack of national political experience.

"We have a young man, Buttigieg," Trump said this month at a Florida campaign rally. "Boot-edge-edge. They say 'edge-edge.'"

"He’s got a great chance. He’ll be great. He’ll be great representing us against President Xi of China," he continued. "That’ll be great."

"You can't get too worried about the name calling and the games he plays," Buttigieg responded the next day. "I was thinking of a Chinese proverb that goes, 'when the wind changes, some people build walls and some people build windmills.'"

Trump also compared Buttigieg to Alfred E. Neuman, the gap-toothed, red-haired and big-eared boy who has appeared on the cover of Mad magazine for decades.

"Alfred E. Neuman cannot become president of the United States," the president said in an interview with Politico.

Buttigieg, 37, shrugged off the nickname, saying “he had to google” it and that it was a “generational thing.”

Former Rep. Beto O’Rourke (D-Texas)

Trump's criticism of the former El Paso congressman has primarily focused on O'Rourke's February rally that rivaled one of his own the same night in the border town.

“A young man who's got very little going for himself except he's got a great first name. He challenged us. We have, say, 35,000 people tonight, and he has, say, 200 people, 300 people," Trump said shortly after the rallies. "Not too good. In fact what I would do, that may be the end of his presidential bid."

Trump revived the criticism this month at a campaign rally.

“I went to Texas and I made a speech, and Beto, Beto, boy has he fallen like a rock," Trump said at the Florida rally. "What the hell happened to Beto?”

“His crowd was not massive, he had like 502 people according to the people who count crowds,” the president added.

Trump also slammed O’Rourke during the 2018 midterm elections when O’Rourke ran to unseat Sen. Ted Cruz Rafael (Ted) Edward CruzCruz blocks amended resolution honoring Ginsburg over language about her dying wish Trump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP MORE (R-Texas).

“Beto O’Rourke is a total lightweight compared to Ted Cruz, and he comes nowhere near representing the values and desires of the people of the Great State of Texas. He will never be allowed to turn Texas into Venezuela!” he tweeted.

Beto O’Rourke is a total lightweight compared to Ted Cruz, and he comes nowhere near representing the values and desires of the people of the Great State of Texas. He will never be allowed to turn Texas into Venezuela! — Donald J. Trump (@realDonaldTrump) October 19, 2018

Sen. Kamala Harris Kamala HarrisHarris faces pivotal moment with Supreme Court battle Nearly 40 Democratic senators call for climate change questions in debates Joe Biden has long forgotten North Carolina: Today's visit is too late MORE (D-Calif.)

Trump bashed Harris as “nasty” following her harsh questioning of Attorney General William Barr Bill BarrHarris faces pivotal moment with Supreme Court battle Hillicon Valley: DOJ proposes tech liability shield reform to Congress | Treasury sanctions individuals, groups tied to Russian malign influence activities | House Republican introduces bill to set standards for self-driving cars McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE when he appeared in front of the Senate Judiciary Committee.

“She was probably very nasty,” the president said of Harris on Fox Business, adding that other presidential candidates on the committee were hard on Barr to score “political points.”

Harris shot back the next day that she was simply trying to “pursue justice.”

“We have a president of the United States whose primary interest I think that has been clear as a result of what we know as a result of the Mueller report, his primary interest has been to obstruct justice," Harris said on CNN. "My primary interest is to pursue justice. You can call that whatever name you want, but I think that's what the American people want in a leader.”

Harris's campaign also fundraised off the comments, blasting Trump's "gendered" attack on the senator.

Trump had said a few days prior that Harris has “a little bit of a nasty wit, but that might be it,” when Sean Hannity asked him of his thoughts on the California Democrat.

It was reported earlier this year that Trump and his daughter, Ivanka, had both donated to Harris's California attorney general campaigns in 2011, 2013 and 2014.

Sen. Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (D-N.J.)

Trump has not commented frequently about Booker, but suggested in 2016 that he had personal dirt on the New Jersey Democrat.

“If Cory Booker is the future of the Democratic Party, they have no future! I know more about Cory than he knows about himself,” he tweeted in July 2016.

If Cory Booker is the future of the Democratic Party, they have no future! I know more about Cory than he knows about himself. — Donald J. Trump (@realDonaldTrump) July 26, 2016

Sen. Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (D-N.Y.)

Trump slammed his home state senator in 2017, saying she used to come to his office “begging” for donations.

“Lightweight Senator Kirsten Gillibrand, a total flunky for Chuck Schumer Chuck SchumerCruz blocks amended resolution honoring Ginsburg over language about her dying wish Senate Democrats introduce legislation to probe politicization of pandemic response Schumer interrupted during live briefing by heckler: 'Stop lying to the people' MORE and someone who would come to my office “begging” for campaign contributions not so long ago (and would do anything for them), is now in the ring fighting against Trump. Very disloyal to Bill & Crooked-USED!” he tweeted.

Lightweight Senator Kirsten Gillibrand, a total flunky for Chuck Schumer and someone who would come to my office “begging” for campaign contributions not so long ago (and would do anything for them), is now in the ring fighting against Trump. Very disloyal to Bill & Crooked-USED! — Donald J. Trump (@realDonaldTrump) December 12, 2017

Gillibrand fired back the next day, slamming the smear as “sexist.”

"It was certainly just a sexist smear intended to silence me," she said during an interview with NBC's "Today Show." "And I'm not going to be silenced on this issue. I have heard the testimony of many women, numerous accusers. I believe them and he should resign for that."

Sen. Amy Klobuchar Amy KlobucharSocial media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates MORE (D-Minn.)

Trump has not focused much of his ire on Klobuchar, but use her campaign launch, which coincided with a Minnesota blizzard, to knock both global warming and the senator.

“Well, it happened again. Amy Klobuchar announced that she is running for President, talking proudly of fighting global warming while standing in a virtual blizzard of snow, ice and freezing temperatures. Bad timing. By the end of her speech she looked like a Snowman(woman)!” he tweeted in February.

Well, it happened again. Amy Klobuchar announced that she is running for President, talking proudly of fighting global warming while standing in a virtual blizzard of snow, ice and freezing temperatures. Bad timing. By the end of her speech she looked like a Snowman(woman)! — Donald J. Trump (@realDonaldTrump) February 10, 2019

New York City Mayor Bill de Blasio Bill de BlasioOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right EPA threatens to close New York City office after Trump threats to 'anarchist' cities New Year's Eve in Times Square to be largely virtual amid pandemic MORE

De Blasio just launched his campaign Thursday morning, but swiftly was labeled a “JOKE” by Trump.

“The Dems are getting another beauty to join their group. Bill de Blasio of NYC, considered the worst mayor in the U.S., will supposedly be making an announcement for president today. He is a JOKE, but if you like high taxes & crime, he’s your man. NYC HATES HIM!” Trump tweeted.

The Dems are getting another beauty to join their group. Bill de Blasio of NYC, considered the worst mayor in the U.S., will supposedly be making an announcement for president today. He is a JOKE, but if you like high taxes & crime, he’s your man. NYC HATES HIM! — Donald J. Trump (@realDonaldTrump) May 16, 2019

De Blasio launched his campaign with a stinging broadside of Trump, calling the president a “con.”

“Right now, the federal government is not on the side of working people. And that’s because Donald Trump is playing a big con on America,” de Blasio said on “Good Morning America.”

“I call him Con Don. Every New Yorker knows he’s a con artist. We know his tricks. We know his playbook,” de Blasio continued. “I know how to take him on — I’ve been watching him for decades. He’s trying to convince working Americans he’s on their side. It’s been a lie from day one.”

President Trump has so far refrained from individually jabbing Sen. Michael Bennet Michael Farrand BennetOVERNIGHT ENERGY: House Democrats tee up vote on climate-focused energy bill next week | EPA reappoints controversial leader to air quality advisory committee | Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' Senate Democrats demand White House fire controversial head of public lands agency Next crisis, keep people working and give them raises MORE (D-Colo.), Gov. Steve Bullock Steve BullockMcConnell locks down key GOP votes in Supreme Court fight Senate Democrats demand White House fire controversial head of public lands agency Pence seeks to boost Daines in critical Montana Senate race MORE (D-Mont.), former San Antonio Mayor and Housing and Urban Development Secretary Julián Castro, former Rep. John Delaney John DelaneyCoronavirus Report: The Hill's Steve Clemons interviews Rep. Rodney Davis Eurasia Group founder Ian Bremmer says Trump right on China but wrong on WHO; CDC issues new guidance for large gatherings The Hill's Coronavirus Report: Kansas City Mayor Quinton Lucas says country needs to rethink what 'policing' means; US cases surpass 2 million with no end to pandemic in sight MORE (D-Md.), Rep. Tulsi Gabbard Tulsi GabbardRepublicans call on DOJ to investigate Netflix over 'Cuties' film Hispanic Caucus campaign arm endorses slate of non-Hispanic candidates Gabbard says she 'was not invited to participate in any way' in Democratic convention MORE (D-Hawaii), former Sen. Mike Gravel (D-Alaska), former Gov. John Hickenlooper John HickenlooperCook Political Report shifts Colorado Senate race toward Democrat Willie Nelson playing at virtual fundraiser for Hickenlooper Gardner on court vacancy: Country needs to mourn Ginsburg 'before the politics begin' MORE (D-Colo.), Gov. Jay Inslee Jay Robert InsleeBarr asked prosecutors to explore charging Seattle mayor over protest zone: report Bottom line Oregon senator says Trump's blame on 'forest management' for wildfires is 'just a big and devastating lie' MORE (D-Wash.), Miramar, Fla. Mayor Wayne Messam Wayne Martin MessamKey moments in the 2020 Democratic presidential race so far Wayne Messam suspends Democratic presidential campaign 2020 primary debate guide: Everything you need to know ahead of the November forum MORE (D), Rep. Seth Moulton Seth MoultonThe Hill's Morning Report - Presented by Facebook - Markey defeats Kennedy; Trump lauds America's enforcers in Wisconsin Moulton fends off primary challenges in Massachusetts Portland: The Pentagon should step up or pipe down MORE (D-Mass.), Rep. Tim Ryan Timothy (Tim) RyanNow's the time to make 'Social Emotional Learning' a national priority Mourners gather outside Supreme Court after passing of Ruth Bader Ginsburg Lincoln Project hits Trump for criticizing Goodyear, 'an American company' MORE (D-Ohio), Rep. Eric Swalwell Eric Michael SwalwellSwalwell calls for creation of presidential crimes commission to investigate Trump when he leaves office 'This already exists': Democrats seize on potential Trump executive order on preexisting conditions Swalwell: Barr has taken Michael Cohen's job as Trump's fixer MORE (D-Calif.), author Marianne Williamson Marianne WilliamsonMarianne Williamson discusses speaking at People's Party Convention Fewer people watched opening night of Democratic convention compared to 2016 Marianne Williamson: Democratic convention 'like binge watching a Marriott commercial' MORE and entrepreneur Andrew Yang Andrew YangDoctor who allegedly assaulted Evelyn Yang arrested on federal charges The Hill's Campaign Report: Biden weighs in on police shootings | Who's moderating the debates | Trump trails in post-convention polls Buttigieg launches his own podcast MORE.