U.S. President Donald Trump pitted two of his Democratic presidential rivals against each other on Twitter Thursday in a series of bombastic and insult riddled tweets. Trump appeared to be trying to whip up an inter-party conflict between former New York City Mayor Michael Bloomberg and Vermont Senator Bernie Sanders.

Trump wrote, “Mini Mike is a 5’4” mass of dead energy who does not want to be on the debate stage with these professional politicians. No boxes please. He hates Crazy Bernie and will, with enough money, possibly stop him. Bernie’s people will go nuts!”

Bloomberg quickly hit back, writing, "we know many of the same people in NY. Behind your back they laugh at you & call you a carnival barking clown. They know you inherited a fortune & squandered it with stupid deals and incompetence. I have the record & the resources to defeat you. And I will."

Trump tweeted minutes before a distorted image of Bloomberg with the text, “Mini Mike Bloomberg is a LOSER who has money but can’t debate and has zero presence, you will see. He reminds me of a tiny version of Jeb “Low Energy” Bush, but Jeb has more political skill and has treated the Black community much better than Mini!”

Earlier in the week, Trump sent out a tweet with a clip of resurfaced comments in which Bloomber says the way to bring down murder rates is to “put a lot of cops” in minority neighborhoods because that’s where “all the crime is.” Trump tweeted the audio declaring, “Bloomberg’s a racist.”

Trump later deleted the tweet, but in impromptu remarks to reporters in the Oval Office later Tuesday, he dismissed Bloomberg’s apology for supporting stop and frisk as “disingenuous.”

But Trump himself has long defended the tactic.

In an October 2018 speech to the International Association of Police Chiefs, Trump touted its use in New York under then-Mayor Giuliani, now his personal attorney, and urged Chicago to adopt it.

And in 2013, he defended both the tactic and Bloomberg’s police commissioner, tweeting, “Stop and frisk works. Instead of criticizing @NY_POLICE Chief Ray Kelly, New Yorkers should be thanking him for keeping NY safe.”

The attacks on Bloomberg reflect a growing concern about the billionaire’s candidacy. Indeed, Bloomberg focused the bulk of his statement on Trump, arguing that the president’s attack “reflects his fear over the growing strength of my campaign.”

The president and his campaign team have been warily watching Bloomberg’s spending spree since the former mayor’s entry into the race.

Trump’s campaign manager, Brad Parscale, had previously told staffers he would not worry about Bloomberg until he cracked double digits, which the former mayor has now done in some recent national polls. Parscale told aides recently that the campaign would soon be doing more Bloomberg-centric polling, according to a campaign aide not authorized to speak publicly about private conversations.

Trump has delivered frequent broadsides against Bloomberg, ignoring counsel from some aides, including senior adviser and son-in-law Jared Kushner, to avoid elevating him in a Democratic field that remains unsettled.

Annoyed by Bloomberg’s superior wealth, favorable press and easy entrée into the upper realm of the New York elite that long ago rejected him, Trump has repeatedly attacked the former mayor, including recent digs about his height and golf game. And on Tuesday, he hinted at how much Bloomberg’s wealth remains on his mind when he said in the Oval Office that the former mayor is a “lightweight” and insisted he’d rather run against Bernie Sanders in the general election because the Vermont senator “has real followers.”

Bloomberg, Trump said, is just “buying his way in.”

The Trump campaign also believes that uncertainty in the Democratic field could help chip away at the other party’s advantage with black voters. The campaign has made its own pitch, touting economic growth for minorities since 2016 and highlighting the president’s advocacy for criminal justice reform, including in a highly watched Super Bowl ad.

Though Trump fares unfavorably with African Americans in most polls, the campaign is simultaneously aiming to win over more black voters and to discourage African Americans from turning out for Democrats by convincing them there is little difference between the two parties’ agendas.

Black voters turned out overwhelmingly for Hillary Clinton in 2016 but at a lesser rate than for Barack Obama, contributing to Trump’s slim margin of victory in several battleground states.