The friendly rivalry between Republican presidential candidates Donald Trump and Vivek Ramaswamy took a turn for the worse over the weekend.

On Saturday, two days before the Iowa caucuses kick off the primary season, Trump took to his Truth Social platform to attack Ramaswamy, a biotech entrepreneur, for the first time.

“Very sly, but a vote for Vivek is a vote for the ‘other side’ — don’t get duped by this,” Trump wrote. “Vote for ‘TRUMP,’ don’t waste your vote! Vivek is not MAGA.”

Throughout his campaign, Ramaswamy has praised and defended Trump. He’s called Trump “the best president of the 21st century and vowed, if elected, to pardon the former president from federal prosecution.

Trump has responded by calling Ramaswamy a “smart guy” with “a lot of talent,” leading to speculation that Ramaswamy could be offered a role in a new Trump administration.

On Saturday, Ramaswamy posted to X, formerly Twitter, a photo of himself with some of his supporters in Iowa who were all wearing T-shirts that read, “SAVE TRUMP, VOTE VIVEK.”

According to multiple reports, the photo angered Trump.  

Trump’s Truth Social post seemed to support that. In it, he wrote, “The Biden Indictments against his Political Opponent will never be allowed in this Country,” before falsely adding, “they are already beginning to fall!”

In addition, Trump campaign senior adviser Chris LaCivita shared Ramaswamy's post and called the Republican candidate "this campaigns [sic] number one FRAUD."

"1. Trump doesnt need 'saving,'" LaCivita wrote. "2. If you support @realDonaldTrump you sure as hell dont vote for this FAKE."

Jason Miller, another Trump campaign adviser, told the New York Post it’s “pretty safe to say” Trump’s pick for vice president “won’t be Vivek.”

Ramaswamy responded Saturday night on X to Trump’s attack. He called the criticism “an unfortunate move” by Trump’s campaign advisers and said he would not criticize the former president.

He wrote that he and Iowa voters he’s spoken with are worried that the “system” won’t allow Trump to return to the presidency.

“It seems they will stop at *nothing* to keep him away from power,” Ramaswamy wrote. “I’m worried for Trump. I’m worried for our country.”

He then cited conspiracy theories about the 2020 election and baselessly accused billionaires and the mainstream media of trying to prop up United Nations Ambassador Nikki Haley as part of a greater plot to eliminate Trump and “trot their puppet into the White House.”

According to the final Des Moines Register/NBC News/Mediacom poll for Monday’s Iowa caucuses, 48% of likely caucusgoers say Trump is their first choice, while 8% favor Ramaswamy.

Haley was second in the poll with 20%, and Florida Gov. Ron DeSantis was third with 16%.