In the laundry list of things that Donald Trump did which were considered well outside the conventions of your average presidential campaign, perhaps assigning derogatory nicknames to his primary opponents and eventually to Hillary Clinton may have been one of the most effective. Hillary quickly became known as “Crooked Hillary” among Republicans, and some Bernie Sanders supporters, with Trump repeating it multiple times a day. The name stuck quite a bit in reference to Hillary’s email scandal unfolding during the campaign.

During the primary, Trump attached labels like “Lyin’ Ted” when accusing Ted Cruz of lying about various campaign issues. Cruz became “Beautiful Ted” in 2018 when he and Trump campaigned together, though. Marco Rubio became “Lil’ Marco” at on point, and let’s not forget “Low-Energy Jeb” when referring to Jeb Bush.

These labels tended to stick and tended to burn each candidate to some extent. According to reports within the White House, the 2020 cycle will be no different.

The Associated Press reports that Trump is testing labels for his 2020 Democratic opponents to find the best nicknames he can employ on the campaign trail:

Inside the West Wing and in conversations with outside allies, Trump has been workshopping other attempts to imprint his new adversaries with lasting labels, according to two people on whom the president has tested out the nicknames. They spoke on condition of anonymity to discuss private conversations with the president. He is also testing out lines of attack in public rallies, exploring vulnerabilities he could use against them should they advance to the general election.

No candidate has drawn more commentary and criticism from Trump than Sen. Warren, the liberal Massachusetts Democrat. Warren’s past claims of Native American heritage prompted Trump to brand her “Pocahontas” and he has shown no qualms about deploying racially charged barbs harking back to some of the nation’s darkest abuses.

Wading into a Twitter frenzy over an Instagram video Warren posted after she announced her exploratory committee while sharing a beer with her husband at their kitchen table, Trump jeered: “Best line in the Elizabeth Warren beer catastrophe is, to her husband, ‘Thank you for being here. I’m glad you’re here’ It’s their house, he’s supposed to be there!”

“If Elizabeth Warren, often referred to by me as Pocahontas, did this commercial from Bighorn or Wounded Knee instead of her kitchen, with her husband dressed in full Indian garb, it would have been a smash!” Trump tweeted.

So far, as the AP story mentions, Elizabeth Warren has taken the brunt of it with Trump derisively referring to her as “Pocahontas” as he has for a few years now.

Trump has often referred to Bernie Sanders as “Crazy Bernie,” but that never had quite the same ring to it as “Crooked Hillary.”

Social media will continue to be a big part of Trump’s daily activities when trying to set his narrative against Democrats in 2020:

Trump’s rivals in the 2016 GOP primary learned that lesson as he bedeviled them with name-calling. Trump goaded Sen. Marco Rubio of Florida into making a thinly veiled insult of his manhood that quickly backfired, and weeks later he sucked Texas Sen. Ted Cruz into a brutal back-and-forth about an insult he had leveled at Cruz’s wife.

“The president has an ability to use social media to define his opponents and influence the primary debate in a way no sitting president before him has,” said former White House spokesman Raj Shah. “I expect him to take full advantage.”

Some Democratic candidates are ripe for Trump’s brand of insults by playing into his hand. Warren is probably the best example as she tried to use a DNA test to prove her Native American ancestry, but the attempt failed and instead gave the President more firepower.

Not every candidate is as vulnerable as Warren is. Cory Booker can be a little corny sometimes, and having referred to himself as having a “Spartacus moment” during the Kavanaugh hearings, he has almost created his own label.

Take a candidate like Kamala Harris, however, and tell me where she’s vulnerable in the same way Warren, Booker, or even Cruz or Rubio were? She’s generally even-keeled, doesn’t offer much in the way of mockery, and probably won’t be making as many missteps as her colleagues.

The worst scenario for Trump is that Democrats nominate a candidate who is fairly immune to his brand of ridicule. A candidate without any obvious, mockable flaws.

Joe Biden is another animated character who may be harder for Trump to pin down despite his many gaffes. Biden, on the other hand, would likely be the one sending it right back at Trump.

2016 was a crazy ride and it seems to have redefined what it means to do “opposition research” when that research now consists of figuring out the best way to mock your opponents on social media and during campaign rallies.