Days after his nomination for NASA was pulled by President Donald Trump, Jared Isaacman told investors in his payments company Shift4 that his “brief stint in politics was a thrilling experience.”

Isaacman said in the letter that he was resigning as CEO of Shift4, which he founded in 1999 at age 16, and will assume the role of executive chairman. He had been planning to leave the company if his nomination was confirmed by the Senate. But it never got that far.

In a post on Truth Social over the weekend, Trump said that he was withdrawing Isaacman’s nomination “after a thorough review of prior associations.” The president didn’t indicate what those associations were, though some reports have suggested that it was a reference to Isaacman’s prior donations to Democrats.

“Even knowing the outcome, I would do it all over again,” Isaacman wrote in the letter.

In an episode of the All-In podcast that went live on Wednesday, Isaacman, who has close ties to Elon Musk, indicated that his past donations weren’t likely the reason for Trump’s decision. He noted that his donations were public long before he was nominated, and he described himself as “right-leaning” and a supporter of the president’s agenda.

“I don’t want to play dumb on this,” he said. “I don’t think the timing was much of a coincidence.”

The timing he was referencing was Musk’s official exit from his government service work at the end of May.

In addition to his career in finance, Isaacman has led two private spaceflights through Musk’s SpaceX, in 2021 and 2024, commanding crews on multiday trips around the Earth. Shift4 also invested $27.5 million in SpaceX, according to a 2021 filing.

Musk became one of Trump’s biggest backers and, until last week, was leading the administration’s Department of Government Efficiency (DOGE), tasked with slashing the size of the federal government. With Musk’s official time as a “special government employee” coming to an end because of the 130-day limit, the world’s richest person has quickly turned into a vocal critic of Trump’s massive tax-cut bill.

On Wednesday, Musk ramped up his attacks on the bill that Trump is pushing Congress to pass, claiming it will condemn America to “debt slavery” and urging lawmakers to “KILL the BILL.” A day earlier, Musk slammed what Trump has dubbed the “big, beautiful bill” as a “disgusting abomination.”

Trump’s decision to pull Isaacman’s nomination came before Musk’s latest tirade. But Musk had been distancing himself from the administration in recent weeks.

“You got one person,” Isaacman said on All-In, referring to Trump as the one making the call. He said he doesn’t “know what the trigger was or wasn’t” and said he doesn’t “fault the president for it.”

The White House didn’t immediately respond to a request for comment.

At Shift4, Isaacman said in Wednesday’s letter that he’ll be succeeded as CEO by Taylor Lauber, who started at the company in 2018 and has been serving as president.

“I have been working since I was a teenager and not planning to stop now,” Isaacman wrote. “I love this company, the strategy and our team. As the largest shareholder, I am eager to continue contributing where I believe my efforts will have the most impact.” 

— CNBC’s Lora Kolodny and MacKenzie Sigalos contributed to this report.

WATCH: Elon Musk slams Trump’s spending bill

Apple was dealt a blow in the U.S. Court of Appeals for the Ninth Circuit on Wednesday, as a panel of judges denied the company’s emergency application to halt changes to its App Store that resulted from the company’s legal battle with Epic Games.

Apple “bears the burden of showing that the circumstances justify an exercise of [our] discretion,” according to the order. “After reviewing the relevant factors, we are not persuaded that a stay is appropriate.”

Last month, the iPhone maker asked the appeals court to pause an order from U.S. District Judge Yvonne Gonzalez Rogers that said that Apple could no longer charge a commission on payment links inside its apps nor tell developers how the links should look.

Apple said the ruling from the judge could cost the company “substantial sums.” 

The ruling has already shifted the economics of app development in the U.S. Developers including Amazon and Spotify have been able to update their apps to avoid Apple’s 15% to 30% commission and direct customers to their own websites for payment.

Amazon’s iPhone Kindle app now shows an orange “Get Book” button that links to Amazon.com.

The rejection of Apple’s stay signals that recent changes under the order can stay in place. Apple CEO Tim Cook has said that Apple would appeal Rogers’ ruling.

In April, Rogers found that Apple had violated her original court order from the Epic Games trial, which was originally decided in 2021, that forced Apple to make limited changes to its link-out policy. She issued a new, more expansive ruling, that told Apple to immediately stop imposing its commissions.

The judge also alleged that Apple had misled the court. 

“We are disappointed with the decision not to stay the district court’s order, and we’ll continue to argue our case during the appeals process,” an Apple spokesperson said in a statement. “As we’ve said before, we strongly disagree with the district court’s opinion. Our goal is to ensure the App Store remains an incredible opportunity for developers and a safe and trusted experience for our users.”

“The long national nightmare of the Apple tax is ended,” Epic Games CEO Tim Sweeney posted on social media.

As more parts of the world face intense drought, new technologies are emerging to clean and reuse existing water. Investors are seeing potential for big profits.

Water treatment is expensive. It uses a lot of energy and produces its own waste that gets disposed of at a hefty price. Capture6, a startup in Berkeley, California, says it’s developing a solution, and one with an added benefit to the environment.

Capture6’s technology repurposes industrial and water treatment waste, generating clean water and capturing carbon dioxide from the atmosphere.

“That combination of water treatment, brine management, and carbon capture all at once is part of what makes us unique, what makes our process innovative,” said Capture6 CEO Ethan Cohen-Cole, who co-founded the company in 2021. “We are able to do so at reduced energy costs.”

The process is complex. It starts with the waste from any sort of water treatment process. Once the solids are removed, that waste is called brine, which is leftover water plus concentrated salt – sodium chloride. Treatment facilities usually have to pay to get rid of it.

But Capture6 takes that brine, strips out the fresh water and separates the salt into sodium and chlorine. It then turns the sodium into lye.

“That lye has the really neat property that if you expose it to the air, it will bond with CO2 and strip it from the air, and that’s the punch line to the process,” said Cohen-Cole. “We have processed the waste salt, we’ve returned fresh water to our partner, and we’ve captured CO2 from the air.”

It’s a particularly attractive proposition in areas most in need of clean water. Capture6 is working in Western Australia, South Korea, and in drought-stricken California, at the Palmdale Water District north of Los Angeles. The district is still testing the technology, but is already projecting huge cost savings in its brine management.

“It will save us 10% on that capital cost, as well as saving us 20 to 40% in operational costs,” said Scott Rogers, assistant general manager at Palmdale Water District. “We’re recovering anywhere from 94% to 98% water out of water that would just normally be wasted.”

Rogers says it’s early but when more facilities start using the technology, it will create a circular economy that can benefit the environment.

Capture6 has raised $27.5 million from Tetrad Corporation, Hyundai Motors, Energy Capital Ventures, Elemental Impact and Triple Impact Capital. 

Cohen-Cole says the company’s entire process could run on renewable energy, so all of the CO2 that it captures will be net negative, improving the environment. That allows the company to generate added revenue by selling carbon credits.

It’s just one technology in a growing field of carbon capture, removal and sequestration. Others include direct air capture, burying carbon underground or injecting it into the ocean.

The Trump Administration recently canceled $3.7 billion worth of awards for new technology, including carbon capture, to fight climate change. Capture6 has received funding from the U.S. Department of Energy and from state-level sources including California, according to the company. So far, none of that has been canceled.

— CNBC producer Lisa Rizzolo contributed to this piece.