• Mark Cuban cautioned Tesla CEO Elon Musk against forming an alliance with Donald Trump, because, he said, the Republican presidential nominee may not ultimately repay his political debts.
• Cuban and Musk are on opposite sides of the 2024 presidential election, but each have their eyes on governmental regulatory roles.
• As Musk supports Trump, he has repeatedly raised his hand to lead a new "government efficiency commission" in the hypothetical Republican administration.
• Meanwhile, Cuban, an outspoken surrogate for Vice President Kamala Harris, has suggested he would be open to leading the SEC if she wins the White House.

Billionaire investor Mark Cuban cautioned Tesla CEO Elon Musk on Sunday against forming an alliance with former President Donald Trump, because, he said, the Republican presidential nominee may not ultimately repay his political debts.

"Elon, there will come a time when you need something from Donald Trump," Cuban wrote in an X post to his fellow billionaire. "You will think you will have earned the right to ask and receive. You have been a loyal, faithful soldier for him."

"At the point you need him the most," Cuban continued. "You will find out what so many before you have learned, his loyalty is only to himself.

Cuban's message came in response to an earlier X post from Musk in which the SpaceX CEO amplified a variety of conspiracy theories about Democrats encouraging immigration into battleground states as "a surefire way to win every election."

"If Trump is NOT elected, this will be the last election," Musk wrote.

Musk's endorsement of Trump is a stark reversal from 2022 when he would openly sling insults at the former president on social media.

Cuban's warning to Musk, one billionaire to another, hinted at the implicit bid for governmental favor that wealthy political supporters make when they hitch their wagon to a presidential candidate.

The two billionaires are on opposing sides of the presidential race this election cycle. But both business leaders have their eyes on some level of regulatory control.

Trump, Cuban believes, might not follow through on that exchange for Musk.

Cuban has become an outspoken surrogate for Vice President Kamala Harris and her economic agenda. In recent weeks, he has regularly championed Harris as "better for business," even amid some skepticism about her plan to raise corporate tax rates.

As Cuban ramps up his public support, he is also keeping tabs on a potential new job opportunity at the Securities and Exchange Commission.

"I told her team, put my name in for the SEC, it needs to change," Cuban said on CNBC's "Squawk Box" earlier this month.

Meanwhile, Musk is chasing a new job of his own. Musk has repeatedly floated the creation of a so-called government efficiency commission to crack down on federal spending if Trump wins a second term in the White House. And he has raised his hand to helm such an agency.

Earlier this month, Trump endorsed the government efficiency commission idea and suggested Musk could be a "good one" to lead it.

But the Republican nominee hedged that Musk, a busy CEO of multiple companies, might not have the time for the job, but that he could "consult."